diff --git a/.github/workflows/licence.yml b/.github/workflows/licence.yml
index ec822c68f..3e6bd418b 100644
--- a/.github/workflows/licence.yml
+++ b/.github/workflows/licence.yml
@@ -64,3 +64,9 @@ jobs:
           cd tools/sz_repo_cli
           dart pub get
           lic_ck check-licenses --config ../../licenses_config.yaml --problematic
+
+      - name: Check licenses in website
+        run: |
+          cd website
+          flutter pub get
+          lic_ck check-licenses --config ../licenses_config.yaml --problematic
diff --git a/app/lib/blackboard/blackboard_item.dart b/app/lib/blackboard/blackboard_item.dart
index dc47e3fd5..2e7bffc7f 100644
--- a/app/lib/blackboard/blackboard_item.dart
+++ b/app/lib/blackboard/blackboard_item.dart
@@ -6,6 +6,7 @@
 //
 // SPDX-License-Identifier: EUPL-1.2
 
+import 'package:clock/clock.dart';
 import 'package:cloud_firestore/cloud_firestore.dart';
 import 'package:cloud_firestore_helper/cloud_firestore_helper.dart';
 
@@ -64,7 +65,7 @@ class BlackboardItem {
       title: "",
       text: null,
       pictureURL: "",
-      createdOn: DateTime.now(),
+      createdOn: clock.now(),
       attachments: [],
       sendNotification: true,
       forUsers: {},
diff --git a/app/lib/calendrical_events/models/calendrical_event.dart b/app/lib/calendrical_events/models/calendrical_event.dart
index 9f3feb22d..6b3db9d5a 100644
--- a/app/lib/calendrical_events/models/calendrical_event.dart
+++ b/app/lib/calendrical_events/models/calendrical_event.dart
@@ -13,7 +13,25 @@ import 'package:sharezone/timetable/src/models/lesson.dart';
 import 'package:sharezone/timetable/src/models/lesson_length/lesson_length.dart';
 import 'package:time/time.dart';
 
-import 'calendrical_event_types.dart';
+enum EventType {
+  event('meeting'),
+  exam('exam');
+
+  /// Database key for the event type.
+  final String key;
+
+  const EventType(this.key);
+
+  static EventType fromString(String s) {
+    switch (s) {
+      case 'meeting':
+        return event;
+      case 'exam':
+        return exam;
+    }
+    throw ArgumentError("Couldn't parse $EventType from unkown event type: $s");
+  }
+}
 
 class CalendricalEvent {
   /// The date and time when the event was created.
@@ -25,7 +43,7 @@ class CalendricalEvent {
 
   final String eventID, groupID, authorID;
   final GroupType groupType;
-  final CalendricalEventType eventType;
+  final EventType eventType;
   final Date date;
   final Time startTime, endTime;
   final String title;
@@ -64,7 +82,7 @@ class CalendricalEvent {
       endTime: Time.parse(data['endTime'] as String),
       title: data['title'] as String,
       groupType: GroupType.values.byName(data['groupType'] as String),
-      eventType: getEventTypeFromString(data['eventType'] as String),
+      eventType: EventType.fromString(data['eventType'] as String),
       detail: data['detail'] as String?,
       place: data['place'] as String?,
       sendNotification: (data['sendNotification'] as bool?) ?? false,
@@ -77,7 +95,7 @@ class CalendricalEvent {
       'createdOn': createdOn,
       'groupID': groupID,
       'groupType': groupType.name,
-      'eventType': getEventTypeToString(eventType),
+      'eventType': eventType.key,
       'authorID': authorID,
       'date': date.toDateString,
       'startTime': startTime.time,
@@ -95,7 +113,7 @@ class CalendricalEvent {
     String? groupID,
     String? authorID,
     GroupType? groupType,
-    CalendricalEventType? eventType,
+    EventType? eventType,
     Date? date,
     Time? startTime,
     Time? endTime,
diff --git a/app/lib/calendrical_events/models/calendrical_event_types.dart b/app/lib/calendrical_events/models/calendrical_event_types.dart
deleted file mode 100644
index eda312293..000000000
--- a/app/lib/calendrical_events/models/calendrical_event_types.dart
+++ /dev/null
@@ -1,102 +0,0 @@
-// Copyright (c) 2022 Sharezone UG (haftungsbeschränkt)
-// Licensed under the EUPL-1.2-or-later.
-//
-// You may obtain a copy of the Licence at:
-// https://joinup.ec.europa.eu/software/page/eupl
-//
-// SPDX-License-Identifier: EUPL-1.2
-
-import 'package:flutter/material.dart';
-
-abstract class CalendricalEventType {
-  String get key;
-  String get name;
-  IconData get iconData;
-  Color get color;
-
-  @override
-  bool operator ==(Object? other) {
-    if (identical(this, other)) return true;
-    return other is CalendricalEventType && other.key == key;
-  }
-
-  @override
-  int get hashCode {
-    return key.hashCode;
-  }
-}
-
-CalendricalEventType getEventTypeFromString(String data) {
-  switch (data) {
-    case 'excursion':
-      return Excursion();
-    case 'exam':
-      return Exam();
-    case 'meeting':
-      return Meeting();
-    case 'other':
-      return OtherEventType();
-    default:
-      return OtherEventType();
-  }
-}
-
-String getEventTypeToString(CalendricalEventType? eventType) {
-  return (eventType ?? OtherEventType()).key;
-}
-
-class Excursion extends CalendricalEventType {
-  @override
-  Color color = Colors.blue;
-
-  @override
-  IconData iconData = Icons.trip_origin;
-
-  @override
-  String key = "excursion";
-
-  @override
-  String name = "Ausflug";
-}
-
-class Exam extends CalendricalEventType {
-  @override
-  Color color = Colors.red;
-
-  @override
-  IconData iconData = Icons.note;
-
-  @override
-  String key = "exam";
-
-  @override
-  String name = "Prüfung";
-}
-
-class Meeting extends CalendricalEventType {
-  @override
-  Color color = Colors.orange;
-
-  @override
-  IconData iconData = Icons.note;
-
-  @override
-  String key = "meeting";
-
-  @override
-  String name = "Veranstaltung";
-}
-
-class OtherEventType extends CalendricalEventType {
-  @override
-  Color color = Colors.purple;
-
-  @override
-  IconData iconData = Icons.more_vert;
-
-  @override
-  String key = "other";
-
-  @override
-  String name = "Anderes";
-}
diff --git a/app/lib/calendrical_events/page/past_calendrical_events_page.dart b/app/lib/calendrical_events/page/past_calendrical_events_page.dart
index 973952bb9..1ba48aad9 100644
--- a/app/lib/calendrical_events/page/past_calendrical_events_page.dart
+++ b/app/lib/calendrical_events/page/past_calendrical_events_page.dart
@@ -15,7 +15,6 @@ import 'package:flutter/material.dart';
 import 'package:group_domain_models/group_domain_models.dart';
 import 'package:provider/provider.dart';
 import 'package:sharezone/calendrical_events/models/calendrical_event.dart';
-import 'package:sharezone/calendrical_events/models/calendrical_event_types.dart';
 import 'package:sharezone/calendrical_events/provider/past_calendrical_events_page_controller.dart';
 import 'package:sharezone/calendrical_events/provider/past_calendrical_events_page_controller_factory.dart';
 import 'package:sharezone/sharezone_plus/page/sharezone_plus_page.dart';
@@ -176,7 +175,7 @@ class _SharezonePlusAd extends StatelessWidget {
         detail: null,
         endTime: Time(hour: 12, minute: 0),
         eventID: 'eventId',
-        eventType: Exam(),
+        eventType: EventType.exam,
         groupType: GroupType.course,
         latestEditor: null,
         place: null,
diff --git a/app/lib/changelog/change_database_model.dart b/app/lib/changelog/change_database_model.dart
index 02989a534..0dca75e9f 100644
--- a/app/lib/changelog/change_database_model.dart
+++ b/app/lib/changelog/change_database_model.dart
@@ -6,9 +6,10 @@
 //
 // SPDX-License-Identifier: EUPL-1.2
 
+import 'package:clock/clock.dart';
 import 'package:cloud_firestore/cloud_firestore.dart';
-import 'package:sharezone/changelog/change.dart';
 import 'package:cloud_firestore_helper/cloud_firestore_helper.dart';
+import 'package:sharezone/changelog/change.dart';
 
 class ChangeDatabaseModel {
   final String id;
@@ -32,7 +33,7 @@ class ChangeDatabaseModel {
     return ChangeDatabaseModel._(
       id: "",
       version: "",
-      releaseDate: DateTime.now(),
+      releaseDate: clock.now(),
       newFeatures: [],
       improvements: [],
       fixes: [],
diff --git a/app/lib/comments/comment.dart b/app/lib/comments/comment.dart
index 631f2d6f4..b8d0e53c5 100644
--- a/app/lib/comments/comment.dart
+++ b/app/lib/comments/comment.dart
@@ -6,6 +6,8 @@
 //
 // SPDX-License-Identifier: EUPL-1.2
 
+import 'package:clock/clock.dart';
+
 import 'misc.dart';
 
 class Comment {
@@ -66,7 +68,7 @@ class CommentAge extends Duration {
 
   int get inApproximateYears => (inDays / approximateDaysPerMonth).round();
 
-  DateTime get writtenOnDateTime => DateTime.now().subtract(this);
+  DateTime get writtenOnDateTime => clock.now().subtract(this);
 }
 
 class CommentAuthor {
diff --git a/app/lib/comments/comment_data_models.dart b/app/lib/comments/comment_data_models.dart
index ec4e1ea54..50254763b 100644
--- a/app/lib/comments/comment_data_models.dart
+++ b/app/lib/comments/comment_data_models.dart
@@ -6,9 +6,10 @@
 //
 // SPDX-License-Identifier: EUPL-1.2
 
+import 'package:clock/clock.dart';
 import 'package:cloud_firestore/cloud_firestore.dart';
-import 'package:sharezone/comments/comment.dart';
 import 'package:cloud_firestore_helper/cloud_firestore_helper.dart';
+import 'package:sharezone/comments/comment.dart';
 
 class CommentDataModel {
   final String? id;
@@ -73,8 +74,7 @@ class CommentDataModel {
       author: author.toModel(),
       content: comment,
       ratings: _createRatings(),
-      age: CommentAge.fromDuration(
-          DateTime.now().difference(writtenOn!.toDate())),
+      age: CommentAge.fromDuration(clock.now().difference(writtenOn!.toDate())),
       id: id,
     );
   }
diff --git a/app/lib/dashboard/bloc/dashboard_bloc.dart b/app/lib/dashboard/bloc/dashboard_bloc.dart
index 54e165a97..dd2043af2 100644
--- a/app/lib/dashboard/bloc/dashboard_bloc.dart
+++ b/app/lib/dashboard/bloc/dashboard_bloc.dart
@@ -9,6 +9,7 @@
 import 'dart:async';
 
 import 'package:bloc_base/bloc_base.dart';
+import 'package:clock/clock.dart';
 import 'package:date/date.dart';
 import 'package:design/design.dart';
 import 'package:firebase_hausaufgabenheft_logik/firebase_hausaufgabenheft_logik.dart';
@@ -52,7 +53,7 @@ extension RepeatEveryExtension<T> on Stream<T> {
 class DashboardBloc extends BlocBase {
   final String _uid;
   final todayDateTimeWithoutTime =
-      DateTime(DateTime.now().year, DateTime.now().month, DateTime.now().day);
+      DateTime(clock.now().year, clock.now().month, clock.now().day);
 
   final _unreadBlackboardViewsSubject = BehaviorSubject<List<BlackboardView>>();
   final _unreadBlackboardItemsEmptySubject = BehaviorSubject<bool>();
@@ -152,7 +153,7 @@ class DashboardBloc extends BlocBase {
 
   List<HomeworkDto> _filterUrgentHomeworks(
       List<HomeworkDto> allHomeworks, TypeOfUser typeOfUser) {
-    final now = DateTime.now();
+    final now = clock.now();
     final dayAfterTomorrow = DateTime(now.year, now.month, now.day + 2);
     // Was passiert, wenn der 30. Oktober ist und 2 Tage dazu gezählt werden? Springt es dann auf den 1. November um?
     // Antwort: Springt um auf den 1.November, gechekt, auf wenn der Code unschön ist, besser wäre dayAfterTomorrow = now.add(Duration(days:2))
@@ -286,7 +287,7 @@ extension on DateTime {
   bool get isDayAfterTomorrow => dayAfterTomorrow == withoutTime;
 
   static DateTime get today =>
-      DateTime(DateTime.now().year, DateTime.now().month, DateTime.now().day);
+      DateTime(clock.now().year, clock.now().month, clock.now().day);
   static DateTime get tomorrow =>
       DateTime(today.year, today.month, today.day + 1);
   static DateTime get dayAfterTomorrow =>
diff --git a/app/lib/dashboard/dashboard_page.dart b/app/lib/dashboard/dashboard_page.dart
index 7cd53a19b..1771d73e2 100644
--- a/app/lib/dashboard/dashboard_page.dart
+++ b/app/lib/dashboard/dashboard_page.dart
@@ -10,6 +10,7 @@ import 'dart:developer';
 
 import 'package:analytics/analytics.dart';
 import 'package:bloc_provider/bloc_provider.dart';
+import 'package:clock/clock.dart';
 import 'package:flutter/cupertino.dart';
 import 'package:flutter/foundation.dart';
 import 'package:flutter/material.dart';
diff --git a/app/lib/dashboard/models/homework_view.dart b/app/lib/dashboard/models/homework_view.dart
index 6c058537f..2a6486b57 100644
--- a/app/lib/dashboard/models/homework_view.dart
+++ b/app/lib/dashboard/models/homework_view.dart
@@ -6,6 +6,7 @@
 //
 // SPDX-License-Identifier: EUPL-1.2
 
+import 'package:clock/clock.dart';
 import 'package:firebase_hausaufgabenheft_logik/firebase_hausaufgabenheft_logik.dart';
 import 'package:flutter/material.dart';
 import 'package:group_domain_models/group_domain_models.dart';
@@ -39,7 +40,7 @@ class HomeworkView {
     }
 
     final todayDateTimeWithoutTime =
-        DateTime(DateTime.now().year, DateTime.now().month, DateTime.now().day);
+        DateTime(clock.now().year, clock.now().month, clock.now().day);
     if (dateTime.isBefore(todayDateTimeWithoutTime)) {
       return "Überfällig!";
     } else if (dateTime.isAtSameMomentAs(todayDateTimeWithoutTime)) {
@@ -62,8 +63,8 @@ class HomeworkView {
     final defaultColor = Colors.grey[400]!;
     if (!withUrgentColor) return defaultColor;
 
-    final dayAfterTomorrow = DateTime(
-        DateTime.now().year, DateTime.now().month, DateTime.now().day + 2);
+    final dayAfterTomorrow =
+        DateTime(clock.now().year, clock.now().month, clock.now().day + 2);
     return dateTime.isBefore(dayAfterTomorrow)
         ? Colors.redAccent
         : defaultColor;
diff --git a/app/lib/dashboard/sections/holiday_countdown_section.dart b/app/lib/dashboard/sections/holiday_countdown_section.dart
index dfe601eec..612e4dcab 100644
--- a/app/lib/dashboard/sections/holiday_countdown_section.dart
+++ b/app/lib/dashboard/sections/holiday_countdown_section.dart
@@ -123,8 +123,7 @@ class _HolidayText extends StatelessWidget {
     }
     // For each Holiday create a Widget and add to the list.
     for (var holiday in holidayList) {
-      int daysTillHolidayBeginn =
-          holiday!.start.difference(DateTime.now()).inDays;
+      int daysTillHolidayBeginn = holiday!.start.difference(clock.now()).inDays;
       String holidayTitle = capitalize(holiday.name);
 
       String emoji;
@@ -139,7 +138,7 @@ class _HolidayText extends StatelessWidget {
         emoji = "🎉🎉🙌";
         textWidget = Text("$holidayTitle: JETZT, WOOOOOOO! $emoji");
       } else {
-        int daysTillHolidayEnd = holiday.end.difference(DateTime.now()).inDays;
+        int daysTillHolidayEnd = holiday.end.difference(clock.now()).inDays;
         if (daysTillHolidayEnd == 0) {
           textWidget = Text("$holidayTitle: Letzer Tag 😱");
         } else {
diff --git a/app/lib/dashboard/update_reminder/update_reminder_bloc.dart b/app/lib/dashboard/update_reminder/update_reminder_bloc.dart
index 795a589c9..b29abf79b 100644
--- a/app/lib/dashboard/update_reminder/update_reminder_bloc.dart
+++ b/app/lib/dashboard/update_reminder/update_reminder_bloc.dart
@@ -7,6 +7,7 @@
 // SPDX-License-Identifier: EUPL-1.2
 
 import 'package:bloc_base/bloc_base.dart';
+import 'package:clock/clock.dart';
 import 'package:crash_analytics/crash_analytics.dart';
 import 'package:meta/meta.dart';
 import 'package:sharezone/changelog/change.dart';
@@ -41,7 +42,7 @@ class UpdateReminderBloc extends BlocBase {
       getCurrentVersion: () => platformInformationRetriever.init().then(
           (_) => Version.parse(name: platformInformationRetriever.version)),
       updateGracePeriod: updateGracePeriod,
-      getCurrentDateTime: () => DateTime.now(),
+      getCurrentDateTime: () => clock.now(),
       crashAnalytics: crashAnalytics,
     );
   }
diff --git a/app/lib/feedback/src/cache/feedback_cache.dart b/app/lib/feedback/src/cache/feedback_cache.dart
index 8b8e7cf9e..5bf026bf0 100644
--- a/app/lib/feedback/src/cache/feedback_cache.dart
+++ b/app/lib/feedback/src/cache/feedback_cache.dart
@@ -8,6 +8,7 @@
 
 import 'dart:developer';
 
+import 'package:clock/clock.dart';
 import 'package:key_value_store/key_value_store.dart';
 import 'package:meta/meta.dart';
 
@@ -37,13 +38,13 @@ class FeedbackCache {
     }
 
     final durationPassedFromLastSubmit =
-        lastSubmit.difference(DateTime.now()).abs();
+        lastSubmit.difference(clock.now()).abs();
     if (durationPassedFromLastSubmit < feedbackCooldown) return true;
     return false;
   }
 
   Future<void> setLastSubmit() async {
-    _cache.setString(lastSubmitCacheKey, DateTime.now().toIso8601String());
+    _cache.setString(lastSubmitCacheKey, clock.now().toIso8601String());
   }
 
   Future<DateTime?> _getLastSubmitTime() async {
diff --git a/app/lib/filesharing/logic/firebase_file_uploader/implementation/firebase_file_uploader_impl.dart b/app/lib/filesharing/logic/firebase_file_uploader/implementation/firebase_file_uploader_impl.dart
index d0925a325..d04f6c265 100644
--- a/app/lib/filesharing/logic/firebase_file_uploader/implementation/firebase_file_uploader_impl.dart
+++ b/app/lib/filesharing/logic/firebase_file_uploader/implementation/firebase_file_uploader_impl.dart
@@ -6,6 +6,7 @@
 //
 // SPDX-License-Identifier: EUPL-1.2
 
+import 'package:clock/clock.dart';
 import 'package:cloud_firestore/cloud_firestore.dart';
 import 'package:files_basics/files_models.dart';
 import 'package:files_basics/local_file.dart';
@@ -45,7 +46,7 @@ class FirebaseFileUploaderImplementation {
         ChangeActivity(
           authorID: creatorID,
           authorName: creatorName,
-          changedOn: DateTime.now(),
+          changedOn: clock.now(),
         )
       ],
       name: localFile.getName(),
diff --git a/app/lib/holidays/holiday_bloc.dart b/app/lib/holidays/holiday_bloc.dart
index 1a2ac2fd2..88e61305d 100644
--- a/app/lib/holidays/holiday_bloc.dart
+++ b/app/lib/holidays/holiday_bloc.dart
@@ -9,6 +9,7 @@
 import 'dart:async';
 
 import 'package:bloc_base/bloc_base.dart';
+import 'package:clock/clock.dart';
 import 'package:holidays/holidays.dart';
 import 'package:rxdart/subjects.dart';
 import 'package:sharezone/util/api/user_api.dart';
@@ -34,7 +35,7 @@ class HolidayBloc extends BlocBase {
       {required this.holidayManager,
       required this.stateGateway,
       this.getCurrentTime}) {
-    getCurrentTime ??= () => DateTime.now();
+    getCurrentTime ??= () => clock.now();
 
     final holidaysStream = userState
         // StateEnum.notSelected would result into an UnsupportedStateException
diff --git a/app/lib/homework/parent/homework_page.dart b/app/lib/homework/parent/homework_page.dart
index eb97cf75b..fbf77efb9 100644
--- a/app/lib/homework/parent/homework_page.dart
+++ b/app/lib/homework/parent/homework_page.dart
@@ -11,20 +11,21 @@ import 'dart:developer';
 
 import 'package:analytics/analytics.dart';
 import 'package:bloc_provider/bloc_provider.dart';
+import 'package:clock/clock.dart';
 import 'package:common_domain_models/common_domain_models.dart';
 import 'package:firebase_hausaufgabenheft_logik/firebase_hausaufgabenheft_logik.dart';
 import 'package:flutter/material.dart';
 import 'package:flutter_staggered_animations/flutter_staggered_animations.dart';
-import 'package:sharezone/main/application_bloc.dart';
-import 'package:sharezone/homework/parent/src/homework_page_bloc.dart';
+import 'package:sharezone/homework/homework_dialog/homework_dialog.dart';
 import 'package:sharezone/homework/homework_page_new.dart';
+import 'package:sharezone/homework/parent/src/homework_page_bloc.dart';
+import 'package:sharezone/homework/shared/homework_archived.dart';
+import 'package:sharezone/homework/shared/homework_card.dart';
+import 'package:sharezone/main/application_bloc.dart';
 import 'package:sharezone/navigation/logic/navigation_bloc.dart';
 import 'package:sharezone/navigation/models/navigation_item.dart';
 import 'package:sharezone/navigation/scaffold/app_bar_configuration.dart';
 import 'package:sharezone/navigation/scaffold/sharezone_main_scaffold.dart';
-import 'package:sharezone/homework/shared/homework_archived.dart';
-import 'package:sharezone/homework/homework_dialog/homework_dialog.dart';
-import 'package:sharezone/homework/shared/homework_card.dart';
 import 'package:sharezone_common/translations.dart';
 import 'package:sharezone_widgets/sharezone_widgets.dart';
 import 'package:user/user.dart';
@@ -59,7 +60,7 @@ Future<void> openHomeworkDialogAndShowConfirmationIfSuccessful(
 List<HomeworkDto> getNotArchived(List<HomeworkDto> homeworkList) {
   final List<HomeworkDto> notArchivedHomeworks = <HomeworkDto>[];
   for (var homework in homeworkList) {
-    final int dif = homework.todoUntil.difference(DateTime.now()).inDays;
+    final int dif = homework.todoUntil.difference(clock.now()).inDays;
     if (dif > -1) {
       notArchivedHomeworks.add(homework);
     }
@@ -572,8 +573,8 @@ class _HomeworkListWithCards extends StatelessWidget {
       final List<HomeworkDto> dayAfterTomorrowList = <HomeworkDto>[];
       final List<HomeworkDto> severalDaysList = <HomeworkDto>[];
 
-      DateTime today = DateTime(
-          DateTime.now().year, DateTime.now().month, DateTime.now().day);
+      DateTime today =
+          DateTime(clock.now().year, clock.now().month, clock.now().day);
       for (var homework in homeworkList!) {
         DateTime homeworkDate = DateTime(homework.todoUntil.year,
             homework.todoUntil.month, homework.todoUntil.day);
diff --git a/app/lib/homework/parent/src/homework_page_bloc.dart b/app/lib/homework/parent/src/homework_page_bloc.dart
index c2ed3f4be..5ce3a3284 100644
--- a/app/lib/homework/parent/src/homework_page_bloc.dart
+++ b/app/lib/homework/parent/src/homework_page_bloc.dart
@@ -10,6 +10,7 @@ import 'dart:async';
 import 'dart:developer';
 
 import 'package:bloc_base/bloc_base.dart';
+import 'package:clock/clock.dart';
 import 'package:firebase_hausaufgabenheft_logik/firebase_hausaufgabenheft_logik.dart';
 import 'package:rxdart/subjects.dart';
 import 'package:sharezone/util/api.dart';
@@ -116,8 +117,8 @@ class HomeworkPageBloc extends BlocBase {
       for (HomeworkDto homework in homeworkNotDone) {
         final DateTime homeworkDateTime = DateTime(homework.todoUntil.year,
             homework.todoUntil.month, homework.todoUntil.day);
-        final DateTime todayDateTime = DateTime(
-            DateTime.now().year, DateTime.now().month, DateTime.now().day);
+        final DateTime todayDateTime =
+            DateTime(clock.now().year, clock.now().month, clock.now().day);
         if (homeworkDateTime.isBefore(todayDateTime)) {
           api.homework.changeIsHomeworkDoneTo(homework.id, true);
         }
diff --git a/app/lib/homework/shared/homework_archived.dart b/app/lib/homework/shared/homework_archived.dart
index 76f86829a..cc2195ee4 100644
--- a/app/lib/homework/shared/homework_archived.dart
+++ b/app/lib/homework/shared/homework_archived.dart
@@ -9,12 +9,13 @@
 import 'dart:developer';
 
 import 'package:bloc_provider/bloc_provider.dart';
+import 'package:clock/clock.dart';
 import 'package:firebase_hausaufgabenheft_logik/firebase_hausaufgabenheft_logik.dart';
 import 'package:flutter/material.dart';
-import 'package:sharezone/main/application_bloc.dart';
-import 'package:sharezone/homework/parent/src/homework_page_bloc.dart';
 import 'package:sharezone/homework/parent/homework_page.dart';
+import 'package:sharezone/homework/parent/src/homework_page_bloc.dart';
 import 'package:sharezone/homework/shared/homework_card.dart';
+import 'package:sharezone/main/application_bloc.dart';
 import 'package:sharezone_widgets/sharezone_widgets.dart';
 import 'package:user/user.dart';
 
@@ -63,8 +64,8 @@ class _HomeworkArchivedPageState extends State<HomeworkArchivedPage> {
                   return ShowCenteredError(error: snapshot.error.toString());
                 }
 
-                DateTime today = DateTime(DateTime.now().year,
-                    DateTime.now().month, DateTime.now().day);
+                DateTime today = DateTime(
+                    clock.now().year, clock.now().month, clock.now().day);
                 List<HomeworkDto> homeworkList =
                     snapshot.data!.where((HomeworkDto homework) {
                   DateTime todoUntil = DateTime(homework.todoUntil.year,
diff --git a/app/lib/homework/shared/homework_card.dart b/app/lib/homework/shared/homework_card.dart
index 79f377440..a58a63b8c 100644
--- a/app/lib/homework/shared/homework_card.dart
+++ b/app/lib/homework/shared/homework_card.dart
@@ -8,27 +8,28 @@
 
 import 'package:analytics/analytics.dart';
 import 'package:bloc_provider/bloc_provider.dart';
+import 'package:clock/clock.dart';
 import 'package:common_domain_models/common_domain_models.dart';
 import 'package:firebase_hausaufgabenheft_logik/firebase_hausaufgabenheft_logik.dart';
 import 'package:flutter/material.dart';
 import 'package:group_domain_models/group_domain_models.dart';
 import 'package:intl/intl.dart';
-import 'package:sharezone/main/application_bloc.dart';
-import 'package:sharezone/homework/parent/src/homework_card_bloc.dart';
 import 'package:sharezone/dashboard/models/homework_view.dart';
 import 'package:sharezone/groups/src/pages/course/course_card.dart';
-import 'package:sharezone/homework/teacher/homework_done_by_users_list/homework_completion_user_list_page.dart';
 import 'package:sharezone/homework/homework_details/homework_details.dart';
 import 'package:sharezone/homework/homework_details/homework_details_view_factory.dart';
-import 'package:sharezone/homework/shared/homework_permissions.dart';
 import 'package:sharezone/homework/parent/homework_page.dart';
+import 'package:sharezone/homework/parent/src/homework_card_bloc.dart';
+import 'package:sharezone/homework/shared/delete_homework.dart';
+import 'package:sharezone/homework/shared/homework_permissions.dart';
+import 'package:sharezone/homework/teacher/homework_done_by_users_list/homework_completion_user_list_page.dart';
+import 'package:sharezone/main/application_bloc.dart';
 import 'package:sharezone/report/page/report_page.dart';
 import 'package:sharezone/report/report_icon.dart';
 import 'package:sharezone/report/report_item.dart';
 import 'package:sharezone/submissions/homework_list_submissions_page.dart';
 import 'package:sharezone/util/api/connections_gateway.dart';
 import 'package:sharezone/util/navigation_service.dart';
-import 'package:sharezone/homework/shared/delete_homework.dart';
 import 'package:sharezone_widgets/sharezone_widgets.dart';
 import 'package:user/user.dart';
 
@@ -52,8 +53,8 @@ class HomeworkCard extends StatelessWidget {
     final bloc = HomeworkCardBloc(api, homework!);
     final analytics = BlocProvider.of<SharezoneContext>(context).analytics;
 
-    DateTime tomorrowWithoutTime = DateTime(
-        DateTime.now().year, DateTime.now().month, DateTime.now().day + 1);
+    DateTime tomorrowWithoutTime =
+        DateTime(clock.now().year, clock.now().month, clock.now().day + 1);
     DateTime todoUntilWithoutTime = DateTime(homework!.todoUntil.year,
         homework!.todoUntil.month, homework!.todoUntil.day);
 
diff --git a/app/lib/main/sharezone_bloc_providers.dart b/app/lib/main/sharezone_bloc_providers.dart
index 9bb0b2338..b2c3b5838 100644
--- a/app/lib/main/sharezone_bloc_providers.dart
+++ b/app/lib/main/sharezone_bloc_providers.dart
@@ -546,7 +546,7 @@ class _SharezoneBlocProvidersState extends State<SharezoneBlocProviders> {
         holidayManager: HolidayService(
           HolidayApi(
             holidayApiClient,
-            getCurrentTime: () => DateTime.now(),
+            getCurrentTime: () => clock.now(),
           ),
           HolidayCache(
             FlutterKeyValueStore(widget.blocDependencies.sharedPreferences),
diff --git a/app/lib/report/report_factory.dart b/app/lib/report/report_factory.dart
index 5e862b406..835f782e2 100644
--- a/app/lib/report/report_factory.dart
+++ b/app/lib/report/report_factory.dart
@@ -7,6 +7,7 @@
 // SPDX-License-Identifier: EUPL-1.2
 
 import 'package:bloc_base/bloc_base.dart';
+import 'package:clock/clock.dart';
 import 'package:cloud_firestore/cloud_firestore.dart';
 
 import 'report.dart';
@@ -26,7 +27,7 @@ class ReportFactory extends BlocBase {
       String description, ReportReason reason, ui.ReportItemReference item) {
     validatePath(item.path);
     return Report(
-      createdOn: DateTime.now(),
+      createdOn: clock.now(),
       creatorID: uid,
       description: description,
       reason: reason,
diff --git a/app/lib/settings/src/subpages/timetable/timetable_settings_page.dart b/app/lib/settings/src/subpages/timetable/timetable_settings_page.dart
index 4984636f1..59000d2e0 100644
--- a/app/lib/settings/src/subpages/timetable/timetable_settings_page.dart
+++ b/app/lib/settings/src/subpages/timetable/timetable_settings_page.dart
@@ -7,20 +7,21 @@
 // SPDX-License-Identifier: EUPL-1.2
 
 import 'package:bloc_provider/bloc_provider.dart';
+import 'package:clock/clock.dart';
 import 'package:date/date.dart';
 import 'package:date/weektype.dart';
 import 'package:flutter/gestures.dart';
 import 'package:flutter/material.dart';
 import 'package:numberpicker/numberpicker.dart';
+import 'package:platform_check/platform_check.dart';
+import 'package:sharezone/settings/src/bloc/user_settings_bloc.dart';
 import 'package:sharezone/settings/src/subpages/timetable/bloc/timetable_settings_bloc.dart';
 import 'package:sharezone/settings/src/subpages/timetable/bloc/timetable_settings_bloc_factory.dart';
 import 'package:sharezone/settings/src/subpages/timetable/periods/periods_edit_page.dart';
-import 'package:sharezone/settings/src/bloc/user_settings_bloc.dart';
 import 'package:sharezone/settings/src/subpages/timetable/weekdays/weekdays_edit_page.dart';
 import 'package:sharezone/timetable/src/edit_time.dart';
 import 'package:sharezone/timetable/src/edit_weektype.dart';
 import 'package:sharezone/timetable/src/models/lesson_length/lesson_length.dart';
-import 'package:platform_check/platform_check.dart';
 import 'package:sharezone_widgets/sharezone_widgets.dart';
 import 'package:time/time.dart';
 import 'package:user/user.dart';
@@ -112,7 +113,7 @@ class _ABWeekField extends StatelessWidget {
                     Padding(
                       padding: const EdgeInsets.fromLTRB(16, 0, 16, 12),
                       child: Text(
-                        "Diese Woche ist Kalenderwoche ${getWeekNumber(DateTime.now()).toString()}. A-Wochen sind ${_getAWeekIsEvenOrOddName(userSettings.isAWeekEvenWeek)} Kalenderwochen und somit ist aktuell eine ${_getCurrentWeekTypeName(userSettings.isAWeekEvenWeek)}.",
+                        "Diese Woche ist Kalenderwoche ${getWeekNumber(clock.now()).toString()}. A-Wochen sind ${_getAWeekIsEvenOrOddName(userSettings.isAWeekEvenWeek)} Kalenderwochen und somit ist aktuell eine ${_getCurrentWeekTypeName(userSettings.isAWeekEvenWeek)}.",
                         textAlign: TextAlign.left,
                         style:
                             const TextStyle(fontSize: 12, color: Colors.grey),
@@ -137,7 +138,7 @@ class _ABWeekField extends StatelessWidget {
   }
 
   WeekType _getCurrentWeekType(bool isAWeekEvenWeek) {
-    final isCurrentWeekEven = getWeekNumber(DateTime.now()).isEven;
+    final isCurrentWeekEven = getWeekNumber(clock.now()).isEven;
     if (isCurrentWeekEven) {
       return isAWeekEvenWeek ? WeekType.a : WeekType.b;
     } else {
diff --git a/app/lib/submissions/homework_list_submissions_page.dart b/app/lib/submissions/homework_list_submissions_page.dart
index 828efa15f..32ddf6a0f 100644
--- a/app/lib/submissions/homework_list_submissions_page.dart
+++ b/app/lib/submissions/homework_list_submissions_page.dart
@@ -8,6 +8,7 @@
 
 import 'package:abgabe_client_lib/abgabe_client_lib.dart';
 import 'package:bloc_provider/bloc_provider.dart';
+import 'package:clock/clock.dart';
 import 'package:files_basics/files_models.dart';
 import 'package:flutter/material.dart';
 import 'package:intl/intl.dart';
@@ -136,14 +137,14 @@ class _LoadingPlaceholder extends StatelessWidget {
               abbreviation: 'A',
               username: 'Patrick Star',
               submittedFiles: [],
-              lastActionDateTime: DateTime.now(),
+              lastActionDateTime: clock.now(),
               wasEditedAfterwards: false,
             ),
             CreatedSubmissionView(
               abbreviation: 'S',
               username: 'Spongebob Schwammkopf',
               submittedFiles: [],
-              lastActionDateTime: DateTime.now(),
+              lastActionDateTime: clock.now(),
               wasEditedAfterwards: false,
             ),
           ], afterDeadlineSubmissions: [
@@ -151,7 +152,7 @@ class _LoadingPlaceholder extends StatelessWidget {
               abbreviation: 'B',
               username: 'Thaddäus Tentakel',
               submittedFiles: [],
-              lastActionDateTime: DateTime.now(),
+              lastActionDateTime: clock.now(),
               wasEditedAfterwards: false,
             ),
           ], missingSubmissions: [
diff --git a/app/lib/timetable/src/edit_date.dart b/app/lib/timetable/src/edit_date.dart
index 25de58e95..c04c4f324 100644
--- a/app/lib/timetable/src/edit_date.dart
+++ b/app/lib/timetable/src/edit_date.dart
@@ -6,6 +6,7 @@
 //
 // SPDX-License-Identifier: EUPL-1.2
 
+import 'package:clock/clock.dart';
 import 'package:date/date.dart';
 import 'package:flutter/material.dart';
 
@@ -76,7 +77,7 @@ Future<Date?> selectDate(
 }) async {
   return showDatePicker(
     context: context,
-    initialDate: initialDate?.toDateTime ?? DateTime.now(),
+    initialDate: initialDate?.toDateTime ?? clock.now(),
     firstDate: Date("2019-01-01").toDateTime,
     lastDate: Date("2029-12-31").toDateTime,
   ).then((newDateTime) {
diff --git a/app/lib/timetable/src/widgets/events/calender_event_card.dart b/app/lib/timetable/src/widgets/events/calender_event_card.dart
index bf5a6ae5b..1d6a1f789 100644
--- a/app/lib/timetable/src/widgets/events/calender_event_card.dart
+++ b/app/lib/timetable/src/widgets/events/calender_event_card.dart
@@ -8,10 +8,9 @@
 
 import 'package:bloc_provider/bloc_provider.dart';
 import 'package:flutter/material.dart';
-import 'package:sharezone/main/application_bloc.dart';
 import 'package:sharezone/calendrical_events/models/calendrical_event.dart';
-import 'package:sharezone/calendrical_events/models/calendrical_event_types.dart';
 import 'package:sharezone/groups/src/pages/course/course_edit/design/course_edit_design.dart';
+import 'package:sharezone/main/application_bloc.dart';
 import 'package:sharezone/report/page/report_page.dart';
 import 'package:sharezone/report/report_icon.dart';
 import 'package:sharezone/report/report_item.dart';
@@ -112,7 +111,7 @@ Future<void> onEventLongPress(
   final isAuthor = api.uID == event.authorID;
   final hasPermissionsToManageEvents = hasPermissionToManageEvents(
       api.course.getRoleFromCourseNoSync(event.groupID)!, isAuthor);
-  final isExam = event.eventType == Exam();
+  final isExam = event.eventType == EventType.exam;
   final result = await showLongPressAdaptiveDialog<_EventLongPressResult>(
     context: context,
     title: "${isExam ? "Prüfung" : "Termin"}: ${event.title}",
diff --git a/app/lib/timetable/timetable_add_event/src/timetable_add_event_event_dialog_api.dart b/app/lib/timetable/timetable_add_event/src/timetable_add_event_event_dialog_api.dart
index f302a4f1e..3d4793eff 100644
--- a/app/lib/timetable/timetable_add_event/src/timetable_add_event_event_dialog_api.dart
+++ b/app/lib/timetable/timetable_add_event/src/timetable_add_event_event_dialog_api.dart
@@ -11,10 +11,12 @@ import 'package:date/date.dart';
 import 'package:equatable/equatable.dart';
 import 'package:group_domain_models/group_domain_models.dart';
 import 'package:sharezone/calendrical_events/models/calendrical_event.dart';
-import 'package:sharezone/calendrical_events/models/calendrical_event_types.dart';
 import 'package:sharezone/util/api.dart';
 import 'package:time/time.dart';
 
+export 'package:sharezone/calendrical_events/models/calendrical_event.dart'
+    show EventType;
+
 class EventDialogApi {
   final SharezoneGateway _api;
 
@@ -33,10 +35,7 @@ class EventDialogApi {
       createdOn: null,
       groupID: command.courseId.id,
       groupType: GroupType.course,
-      eventType: switch (command.eventType) {
-        EventType.event => Meeting(),
-        EventType.exam => Exam(),
-      },
+      eventType: command.eventType,
       date: command.date,
       place: command.location,
       startTime: command.startTime,
@@ -52,8 +51,6 @@ class EventDialogApi {
   }
 }
 
-enum EventType { event, exam }
-
 class CreateEventCommand extends Equatable {
   final String title;
   final CourseId courseId;
diff --git a/app/lib/timetable/timetable_edit/event/timetable_event_edit_page.dart b/app/lib/timetable/timetable_edit/event/timetable_event_edit_page.dart
index 888d5d648..8f4711c55 100644
--- a/app/lib/timetable/timetable_edit/event/timetable_event_edit_page.dart
+++ b/app/lib/timetable/timetable_edit/event/timetable_event_edit_page.dart
@@ -12,9 +12,8 @@ import 'package:bloc_provider/bloc_provider.dart';
 import 'package:date/date.dart';
 import 'package:flutter/material.dart';
 import 'package:group_domain_models/group_domain_models.dart';
-import 'package:sharezone/main/application_bloc.dart';
 import 'package:sharezone/calendrical_events/models/calendrical_event.dart';
-import 'package:sharezone/calendrical_events/models/calendrical_event_types.dart';
+import 'package:sharezone/main/application_bloc.dart';
 import 'package:sharezone/markdown/markdown_analytics.dart';
 import 'package:sharezone/markdown/markdown_support.dart';
 import 'package:sharezone/timetable/src/edit_date.dart';
@@ -90,7 +89,7 @@ class _TimetableEditEventPage extends StatelessWidget {
 
   @override
   Widget build(BuildContext context) {
-    final isExam = initialEvent.eventType == Exam();
+    final isExam = initialEvent.eventType == EventType.exam;
     return PopScope(
       canPop: false,
       onPopInvoked: (didPop) async {
@@ -354,7 +353,7 @@ class _DetailField extends StatelessWidget {
 
   @override
   Widget build(BuildContext context) {
-    final isExam = initialEvent.eventType == Exam();
+    final isExam = initialEvent.eventType == EventType.exam;
     final bloc = BlocProvider.of<TimetableEditEventBloc>(context);
     return Padding(
       padding: const EdgeInsets.only(top: 10),
diff --git a/app/lib/timetable/timetable_page/timetable_event_details.dart b/app/lib/timetable/timetable_page/timetable_event_details.dart
index 93df78535..d0924d7b1 100644
--- a/app/lib/timetable/timetable_page/timetable_event_details.dart
+++ b/app/lib/timetable/timetable_page/timetable_event_details.dart
@@ -13,10 +13,10 @@ import 'package:design/design.dart';
 import 'package:flutter/material.dart';
 import 'package:flutter_markdown/flutter_markdown.dart';
 import 'package:flutter_native_timezone/flutter_native_timezone.dart';
+import 'package:platform_check/platform_check.dart';
 import 'package:provider/provider.dart';
-import 'package:sharezone/main/application_bloc.dart';
 import 'package:sharezone/calendrical_events/models/calendrical_event.dart';
-import 'package:sharezone/calendrical_events/models/calendrical_event_types.dart';
+import 'package:sharezone/main/application_bloc.dart';
 import 'package:sharezone/report/page/report_page.dart';
 import 'package:sharezone/report/report_icon.dart';
 import 'package:sharezone/report/report_item.dart';
@@ -26,7 +26,6 @@ import 'package:sharezone/timetable/timetable_edit/event/timetable_event_edit_pa
 import 'package:sharezone/timetable/timetable_permissions.dart';
 import 'package:sharezone/util/launch_link.dart';
 import 'package:sharezone/util/navigation_service.dart';
-import 'package:platform_check/platform_check.dart';
 import 'package:sharezone_widgets/sharezone_widgets.dart';
 
 enum _EventModelSheetAction { edit, delete, report }
@@ -152,7 +151,7 @@ class _TimetableEventDetailsPage extends StatelessWidget {
     final isAuthor = api.uID == event.authorID;
     final hasPermissionsToManageLessons = hasPermissionToManageEvents(
         api.course.getRoleFromCourseNoSync(event.groupID)!, isAuthor);
-    final isExam = event.eventType == Exam();
+    final isExam = event.eventType == EventType.exam;
     final theme = Theme.of(context);
 
     return Scaffold(
@@ -198,11 +197,6 @@ class _TimetableEventDetailsPage extends StatelessWidget {
                     ),
                   ),
                 ),
-                if (event.eventType is OtherEventType == false)
-                  ListTile(
-                    leading: const Icon(Icons.label),
-                    title: Text("Art: ${event.eventType.name}"),
-                  ),
                 ListTile(
                   leading: const Icon(Icons.place),
                   title: Text("Raum: ${event.place ?? "-"}"),
diff --git a/app/lib/util/api/homework_api.dart b/app/lib/util/api/homework_api.dart
index fcdd260e7..b81fbb910 100644
--- a/app/lib/util/api/homework_api.dart
+++ b/app/lib/util/api/homework_api.dart
@@ -9,6 +9,7 @@
 import 'dart:async';
 import 'dart:developer';
 
+import 'package:clock/clock.dart';
 import 'package:cloud_firestore/cloud_firestore.dart';
 import 'package:filesharing_logic/filesharing_logic_models.dart';
 import 'package:firebase_hausaufgabenheft_logik/firebase_hausaufgabenheft_logik.dart';
@@ -54,7 +55,7 @@ class HomeworkGateway {
 
   Future<void> _setUpStreams(
       FirebaseFirestore firestore, TypeOfUser typeOfUser) async {
-    final now = DateTime.now();
+    final now = clock.now();
     final startOfThisDay = DateTime(now.year, now.month, now.day);
 
     if (typeOfUser == TypeOfUser.student) {
diff --git a/app/test/feedback/feedback_cache_test.dart b/app/test/feedback/feedback_cache_test.dart
index b8886fb9e..3482f1b46 100644
--- a/app/test/feedback/feedback_cache_test.dart
+++ b/app/test/feedback/feedback_cache_test.dart
@@ -6,6 +6,7 @@
 //
 // SPDX-License-Identifier: EUPL-1.2
 
+import 'package:clock/clock.dart';
 import 'package:flutter_test/flutter_test.dart';
 import 'package:key_value_store/in_memory_key_value_store.dart';
 import 'package:sharezone/feedback/src/cache/feedback_cache.dart';
@@ -29,7 +30,7 @@ void main() {
         "Returns no cooldown if cached last send time is more than cooldown range",
         () async {
       const cooldownDuration = Duration(minutes: 2);
-      final lastFeedbackSend = DateTime.now().subtract(cooldownDuration +
+      final lastFeedbackSend = clock.now().subtract(cooldownDuration +
           const Duration(seconds: 10)); // So Feedback should get no cooldown
 
       dummyKeyValueStore.setString(
@@ -44,7 +45,7 @@ void main() {
         "Returns cooldown if cached last send time is less than cooldown range",
         () async {
       const cooldownDuration = Duration(minutes: 2);
-      final lastFeedbackSend = DateTime.now().subtract(cooldownDuration -
+      final lastFeedbackSend = clock.now().subtract(cooldownDuration -
           const Duration(seconds: 10)); // So Feedback should get cooldown
 
       await dummyKeyValueStore.setString(
diff --git a/app/test/holidays/holiday_bloc_unit_test.dart b/app/test/holidays/holiday_bloc_unit_test.dart
index 05379e6a6..ec065701e 100644
--- a/app/test/holidays/holiday_bloc_unit_test.dart
+++ b/app/test/holidays/holiday_bloc_unit_test.dart
@@ -6,6 +6,7 @@
 //
 // SPDX-License-Identifier: EUPL-1.2
 
+import 'package:clock/clock.dart';
 import 'package:flutter_test/flutter_test.dart';
 import 'package:holidays/holidays.dart';
 import 'package:mockito/annotations.dart';
@@ -175,7 +176,7 @@ class InMemoryHolidayStateGateway extends HolidayStateGateway {
 List<Holiday> generateHolidayList(int length) {
   List<Holiday> holidays = [];
   for (int i = 0; i < length; i++) {
-    final start = DateTime.now().add(Duration(days: i + 1));
+    final start = clock.now().add(Duration(days: i + 1));
     final end = start.add(Duration(days: i + 4));
     holidays.add(generateHoliday(start, end));
   }
diff --git a/app/test/holidays/holiday_cache_test.dart b/app/test/holidays/holiday_cache_test.dart
index 94bc2c696..bf0c5eef5 100644
--- a/app/test/holidays/holiday_cache_test.dart
+++ b/app/test/holidays/holiday_cache_test.dart
@@ -7,6 +7,7 @@
 // SPDX-License-Identifier: EUPL-1.2
 
 import 'package:built_collection/built_collection.dart';
+import 'package:clock/clock.dart';
 import "package:flutter_test/flutter_test.dart";
 import 'package:holidays/holidays.dart';
 import 'package:key_value_store/in_memory_key_value_store.dart';
@@ -37,14 +38,14 @@ void main() {
     State state = const NordrheinWestfalen();
 
     Holiday holidayInTheFuture = generateHoliday(
-        DateTime.now().add(const Duration(days: 1)),
-        DateTime.now().add(const Duration(days: 5)));
+        clock.now().add(const Duration(days: 1)),
+        clock.now().add(const Duration(days: 5)));
     Holiday holidayInThePast = generateHoliday(
-        DateTime.now().subtract(const Duration(days: 10)),
-        DateTime.now().subtract(const Duration(days: 5)));
+        clock.now().subtract(const Duration(days: 10)),
+        clock.now().subtract(const Duration(days: 5)));
     holidayCacheData = HolidayCacheData((b) => b
       ..holidays = ListBuilder([holidayInThePast, holidayInTheFuture])
-      ..saved = DateTime.now());
+      ..saved = clock.now());
     kVstore.setString(
         HolidayCache.getKeyString(state), holidayCacheData.toJson());
 
@@ -66,8 +67,8 @@ void main() {
       expect(cacheResponse.inValidTimeframe, true);
     });
     test("Correctly returns false", () async {
-      final sixtyDaysBefore = DateTime.now().subtract(const Duration(days: 60));
-      final now = DateTime.now();
+      final sixtyDaysBefore = clock.now().subtract(const Duration(days: 60));
+      final now = clock.now();
       var currentTimeReturnedToCache = sixtyDaysBefore;
       HolidayCache cache = HolidayCache(kVstore,
           getCurrentTime: () => currentTimeReturnedToCache);
diff --git a/app/test/holidays/integration_test.dart b/app/test/holidays/integration_test.dart
index ef379590c..68fd2bcb6 100644
--- a/app/test/holidays/integration_test.dart
+++ b/app/test/holidays/integration_test.dart
@@ -74,7 +74,7 @@ HolidayBloc setupBloc(MockSharezoneAppFunctions szAppFunctions,
   HolidayApi api = HolidayApi(
     CloudFunctionHolidayApiClient(szAppFunctions),
     getCurrentTime: () => currentTime,
-  ); // Return ended Holidays, as I can't manipulate DateTime.now(). This would lead to flaky tests.
+  ); // Return ended Holidays, as I can't manipulate clock.now(). This would lead to flaky tests.
   InMemoryKeyValueStore keyValueStore = InMemoryKeyValueStore();
   HolidayCache cache =
       HolidayCache(keyValueStore, getCurrentTime: () => currentTime);
diff --git a/app/test/timetable/timetable_bloc_test.dart b/app/test/timetable/timetable_bloc_test.dart
index d1e5c1a3c..7d33f05e6 100644
--- a/app/test/timetable/timetable_bloc_test.dart
+++ b/app/test/timetable/timetable_bloc_test.dart
@@ -6,6 +6,7 @@
 //
 // SPDX-License-Identifier: EUPL-1.2
 
+import 'package:clock/clock.dart';
 import 'package:common_domain_models/common_domain_models.dart';
 import 'package:date/src/date.dart';
 import 'package:date/weekday.dart';
@@ -13,7 +14,6 @@ import 'package:date/weektype.dart';
 import 'package:flutter_test/flutter_test.dart';
 import 'package:group_domain_models/group_domain_models.dart';
 import 'package:sharezone/calendrical_events/models/calendrical_event.dart';
-import 'package:sharezone/calendrical_events/models/calendrical_event_types.dart';
 import 'package:sharezone/timetable/src/bloc/timetable_bloc.dart';
 import 'package:sharezone/timetable/src/models/lesson.dart';
 import 'package:sharezone/timetable/timetable_page/school_class_filter/school_class_filter_view.dart';
@@ -54,8 +54,8 @@ void main() {
         teacher: "",
         weekday: WeekDay.monday,
         weektype: WeekType.always,
-        startDate: Date.fromDateTime(DateTime.now()),
-        endDate: Date.fromDateTime(DateTime.now()),
+        startDate: Date.fromDateTime(clock.now()),
+        endDate: Date.fromDateTime(clock.now()),
       );
     }
 
@@ -71,7 +71,7 @@ void main() {
         date: Date.today(),
         detail: '',
         eventID: 'eventId',
-        eventType: Meeting(),
+        eventType: EventType.event,
         latestEditor: '',
         sendNotification: false,
         title: 'title',
diff --git a/app/test_goldens/calendrical_events/page/past_calendrical_events_page_test.dart b/app/test_goldens/calendrical_events/page/past_calendrical_events_page_test.dart
index bdfe013f8..ba2048341 100644
--- a/app/test_goldens/calendrical_events/page/past_calendrical_events_page_test.dart
+++ b/app/test_goldens/calendrical_events/page/past_calendrical_events_page_test.dart
@@ -104,11 +104,15 @@ void main() {
 
     group('without Sharezone Plus', () {
       setUp(() {
-        when(controller.state).thenReturn(
-          const PastCalendricalEventsPageNotUnlockedState(
-            sortingOrder: EventsSortingOrder.descending,
-          ),
+        const state = PastCalendricalEventsPageNotUnlockedState(
+          sortingOrder: EventsSortingOrder.descending,
         );
+        // Mockito does not support mocking sealed classes yet, so we have to
+        // provide a dummy implementation of the state.
+        //
+        // Ticket: https://github.com/dart-lang/mockito/issues/675
+        provideDummy<PastCalendricalEventsPageState>(state);
+        when(controller.state).thenReturn(state);
       });
 
       testGoldens('renders correctly (light theme)', (tester) async {
diff --git a/app/test_goldens/calendrical_events/page/past_calendrical_events_page_test.mocks.dart b/app/test_goldens/calendrical_events/page/past_calendrical_events_page_test.mocks.dart
index 51d60888c..ebf2ee136 100644
--- a/app/test_goldens/calendrical_events/page/past_calendrical_events_page_test.mocks.dart
+++ b/app/test_goldens/calendrical_events/page/past_calendrical_events_page_test.mocks.dart
@@ -3,31 +3,29 @@
 // Do not manually edit this file.
 
 // ignore_for_file: no_leading_underscores_for_library_prefixes
-import 'dart:ui' as _i16;
+import 'dart:ui' as _i15;
 
 import 'package:clock/clock.dart' as _i6;
-import 'package:date/date.dart' as _i10;
-import 'package:group_domain_models/group_domain_models.dart' as _i17;
+import 'package:date/date.dart' as _i9;
+import 'package:group_domain_models/group_domain_models.dart' as _i16;
 import 'package:mockito/mockito.dart' as _i1;
-import 'package:mockito/src/dummies.dart' as _i15;
+import 'package:mockito/src/dummies.dart' as _i14;
 import 'package:sharezone/calendrical_events/analytics/past_calendrical_events_page_analytics.dart'
     as _i7;
 import 'package:sharezone/calendrical_events/models/calendrical_event.dart'
-    as _i13;
-import 'package:sharezone/calendrical_events/models/calendrical_event_types.dart'
-    as _i9;
+    as _i12;
 import 'package:sharezone/calendrical_events/provider/past_calendrical_events_page_controller.dart'
     as _i8;
 import 'package:sharezone/calendrical_events/provider/past_calendrical_events_page_controller_factory.dart'
-    as _i14;
+    as _i13;
 import 'package:sharezone/sharezone_plus/subscription_service/subscription_service.dart'
     as _i2;
 import 'package:sharezone/timetable/src/models/lesson_length/lesson_length.dart'
-    as _i12;
+    as _i11;
 import 'package:sharezone/util/api/course_gateway.dart' as _i4;
 import 'package:sharezone/util/api/school_class_gateway.dart' as _i5;
 import 'package:sharezone/util/api/timetable_gateway.dart' as _i3;
-import 'package:time/time.dart' as _i11;
+import 'package:time/time.dart' as _i10;
 
 // ignore_for_file: type=lint
 // ignore_for_file: avoid_redundant_argument_values
@@ -117,19 +115,8 @@ class _FakePastCalendricalEventsPageController_6 extends _i1.SmartFake
         );
 }
 
-class _FakeCalendricalEventType_7 extends _i1.SmartFake
-    implements _i9.CalendricalEventType {
-  _FakeCalendricalEventType_7(
-    Object parent,
-    Invocation parentInvocation,
-  ) : super(
-          parent,
-          parentInvocation,
-        );
-}
-
-class _FakeDate_8 extends _i1.SmartFake implements _i10.Date {
-  _FakeDate_8(
+class _FakeDate_7 extends _i1.SmartFake implements _i9.Date {
+  _FakeDate_7(
     Object parent,
     Invocation parentInvocation,
   ) : super(
@@ -138,8 +125,8 @@ class _FakeDate_8 extends _i1.SmartFake implements _i10.Date {
         );
 }
 
-class _FakeTime_9 extends _i1.SmartFake implements _i11.Time {
-  _FakeTime_9(
+class _FakeTime_8 extends _i1.SmartFake implements _i10.Time {
+  _FakeTime_8(
     Object parent,
     Invocation parentInvocation,
   ) : super(
@@ -148,8 +135,8 @@ class _FakeTime_9 extends _i1.SmartFake implements _i11.Time {
         );
 }
 
-class _FakeLessonLength_10 extends _i1.SmartFake implements _i12.LessonLength {
-  _FakeLessonLength_10(
+class _FakeLessonLength_9 extends _i1.SmartFake implements _i11.LessonLength {
+  _FakeLessonLength_9(
     Object parent,
     Invocation parentInvocation,
   ) : super(
@@ -158,8 +145,8 @@ class _FakeLessonLength_10 extends _i1.SmartFake implements _i12.LessonLength {
         );
 }
 
-class _FakeDateTime_11 extends _i1.SmartFake implements DateTime {
-  _FakeDateTime_11(
+class _FakeDateTime_10 extends _i1.SmartFake implements DateTime {
+  _FakeDateTime_10(
     Object parent,
     Invocation parentInvocation,
   ) : super(
@@ -168,9 +155,9 @@ class _FakeDateTime_11 extends _i1.SmartFake implements DateTime {
         );
 }
 
-class _FakeCalendricalEvent_12 extends _i1.SmartFake
-    implements _i13.CalendricalEvent {
-  _FakeCalendricalEvent_12(
+class _FakeCalendricalEvent_11 extends _i1.SmartFake
+    implements _i12.CalendricalEvent {
+  _FakeCalendricalEvent_11(
     Object parent,
     Invocation parentInvocation,
   ) : super(
@@ -183,7 +170,7 @@ class _FakeCalendricalEvent_12 extends _i1.SmartFake
 ///
 /// See the documentation for Mockito's code generation for more information.
 class MockPastCalendricalEventsPageControllerFactory extends _i1.Mock
-    implements _i14.PastCalendricalEventsPageControllerFactory {
+    implements _i13.PastCalendricalEventsPageControllerFactory {
   @override
   _i2.SubscriptionService get subscriptionService => (super.noSuchMethod(
         Invocation.getter(#subscriptionService),
@@ -287,12 +274,12 @@ class MockPastCalendricalEventsPageController extends _i1.Mock
   @override
   _i8.PastCalendricalEventsPageState get state => (super.noSuchMethod(
         Invocation.getter(#state),
-        returnValue: _i15.dummyValue<_i8.PastCalendricalEventsPageState>(
+        returnValue: _i14.dummyValue<_i8.PastCalendricalEventsPageState>(
           this,
           Invocation.getter(#state),
         ),
         returnValueForMissingStub:
-            _i15.dummyValue<_i8.PastCalendricalEventsPageState>(
+            _i14.dummyValue<_i8.PastCalendricalEventsPageState>(
           this,
           Invocation.getter(#state),
         ),
@@ -376,7 +363,7 @@ class MockPastCalendricalEventsPageController extends _i1.Mock
         returnValueForMissingStub: null,
       );
   @override
-  void addListener(_i16.VoidCallback? listener) => super.noSuchMethod(
+  void addListener(_i15.VoidCallback? listener) => super.noSuchMethod(
         Invocation.method(
           #addListener,
           [listener],
@@ -384,7 +371,7 @@ class MockPastCalendricalEventsPageController extends _i1.Mock
         returnValueForMissingStub: null,
       );
   @override
-  void removeListener(_i16.VoidCallback? listener) => super.noSuchMethod(
+  void removeListener(_i15.VoidCallback? listener) => super.noSuchMethod(
         Invocation.method(
           #removeListener,
           [listener],
@@ -404,15 +391,15 @@ class MockPastCalendricalEventsPageController extends _i1.Mock
 /// A class which mocks [CalendricalEvent].
 ///
 /// See the documentation for Mockito's code generation for more information.
-class MockCalendricalEvent extends _i1.Mock implements _i13.CalendricalEvent {
+class MockCalendricalEvent extends _i1.Mock implements _i12.CalendricalEvent {
   @override
   String get eventID => (super.noSuchMethod(
         Invocation.getter(#eventID),
-        returnValue: _i15.dummyValue<String>(
+        returnValue: _i14.dummyValue<String>(
           this,
           Invocation.getter(#eventID),
         ),
-        returnValueForMissingStub: _i15.dummyValue<String>(
+        returnValueForMissingStub: _i14.dummyValue<String>(
           this,
           Invocation.getter(#eventID),
         ),
@@ -420,11 +407,11 @@ class MockCalendricalEvent extends _i1.Mock implements _i13.CalendricalEvent {
   @override
   String get groupID => (super.noSuchMethod(
         Invocation.getter(#groupID),
-        returnValue: _i15.dummyValue<String>(
+        returnValue: _i14.dummyValue<String>(
           this,
           Invocation.getter(#groupID),
         ),
-        returnValueForMissingStub: _i15.dummyValue<String>(
+        returnValueForMissingStub: _i14.dummyValue<String>(
           this,
           Invocation.getter(#groupID),
         ),
@@ -432,77 +419,71 @@ class MockCalendricalEvent extends _i1.Mock implements _i13.CalendricalEvent {
   @override
   String get authorID => (super.noSuchMethod(
         Invocation.getter(#authorID),
-        returnValue: _i15.dummyValue<String>(
+        returnValue: _i14.dummyValue<String>(
           this,
           Invocation.getter(#authorID),
         ),
-        returnValueForMissingStub: _i15.dummyValue<String>(
+        returnValueForMissingStub: _i14.dummyValue<String>(
           this,
           Invocation.getter(#authorID),
         ),
       ) as String);
   @override
-  _i17.GroupType get groupType => (super.noSuchMethod(
+  _i16.GroupType get groupType => (super.noSuchMethod(
         Invocation.getter(#groupType),
-        returnValue: _i17.GroupType.course,
-        returnValueForMissingStub: _i17.GroupType.course,
-      ) as _i17.GroupType);
+        returnValue: _i16.GroupType.course,
+        returnValueForMissingStub: _i16.GroupType.course,
+      ) as _i16.GroupType);
   @override
-  _i9.CalendricalEventType get eventType => (super.noSuchMethod(
+  _i12.EventType get eventType => (super.noSuchMethod(
         Invocation.getter(#eventType),
-        returnValue: _FakeCalendricalEventType_7(
-          this,
-          Invocation.getter(#eventType),
-        ),
-        returnValueForMissingStub: _FakeCalendricalEventType_7(
-          this,
-          Invocation.getter(#eventType),
-        ),
-      ) as _i9.CalendricalEventType);
+        returnValue: _i12.EventType.event,
+        returnValueForMissingStub: _i12.EventType.event,
+      ) as _i12.EventType);
   @override
-  _i10.Date get date => (super.noSuchMethod(
+  _i9.Date get date => (super.noSuchMethod(
         Invocation.getter(#date),
-        returnValue: _FakeDate_8(
+        returnValue: _FakeDate_7(
           this,
           Invocation.getter(#date),
         ),
-        returnValueForMissingStub: _FakeDate_8(
+        returnValueForMissingStub: _FakeDate_7(
           this,
           Invocation.getter(#date),
         ),
-      ) as _i10.Date);
+      ) as _i9.Date);
   @override
-  _i11.Time get startTime => (super.noSuchMethod(
+  _i10.Time get startTime => (super.noSuchMethod(
         Invocation.getter(#startTime),
-        returnValue: _FakeTime_9(
+        returnValue: _FakeTime_8(
           this,
           Invocation.getter(#startTime),
         ),
-        returnValueForMissingStub: _FakeTime_9(
+        returnValueForMissingStub: _FakeTime_8(
           this,
           Invocation.getter(#startTime),
         ),
-      ) as _i11.Time);
+      ) as _i10.Time);
   @override
-  _i11.Time get endTime => (super.noSuchMethod(
+  _i10.Time get endTime => (super.noSuchMethod(
         Invocation.getter(#endTime),
-        returnValue: _FakeTime_9(
+        returnValue: _FakeTime_8(
           this,
           Invocation.getter(#endTime),
         ),
-        returnValueForMissingStub: _FakeTime_9(
+        returnValueForMissingStub: _FakeTime_8(
           this,
           Invocation.getter(#endTime),
         ),
-      ) as _i11.Time);
+      ) as _i10.Time);
   @override
   String get title => (super.noSuchMethod(
         Invocation.getter(#title),
-        returnValue: _i15.dummyValue<String>(
+        returnValue: _i14.dummyValue<String>(
           this,
           Invocation.getter(#title),
         ),
-        returnValueForMissingStub: _i15.dummyValue<String>(
+        returnValueForMissingStub: _i14.dummyValue<String>(
           this,
           Invocation.getter(#title),
         ),
@@ -514,25 +495,25 @@ class MockCalendricalEvent extends _i1.Mock implements _i13.CalendricalEvent {
         returnValueForMissingStub: false,
       ) as bool);
   @override
-  _i12.LessonLength get length => (super.noSuchMethod(
+  _i11.LessonLength get length => (super.noSuchMethod(
         Invocation.getter(#length),
-        returnValue: _FakeLessonLength_10(
+        returnValue: _FakeLessonLength_9(
           this,
           Invocation.getter(#length),
         ),
-        returnValueForMissingStub: _FakeLessonLength_10(
+        returnValueForMissingStub: _FakeLessonLength_9(
           this,
           Invocation.getter(#length),
         ),
-      ) as _i12.LessonLength);
+      ) as _i11.LessonLength);
   @override
   DateTime get startDateTime => (super.noSuchMethod(
         Invocation.getter(#startDateTime),
-        returnValue: _FakeDateTime_11(
+        returnValue: _FakeDateTime_10(
           this,
           Invocation.getter(#startDateTime),
         ),
-        returnValueForMissingStub: _FakeDateTime_11(
+        returnValueForMissingStub: _FakeDateTime_10(
           this,
           Invocation.getter(#startDateTime),
         ),
@@ -540,11 +521,11 @@ class MockCalendricalEvent extends _i1.Mock implements _i13.CalendricalEvent {
   @override
   DateTime get endDateTime => (super.noSuchMethod(
         Invocation.getter(#endDateTime),
-        returnValue: _FakeDateTime_11(
+        returnValue: _FakeDateTime_10(
           this,
           Invocation.getter(#endDateTime),
         ),
-        returnValueForMissingStub: _FakeDateTime_11(
+        returnValueForMissingStub: _FakeDateTime_10(
           this,
           Invocation.getter(#endDateTime),
         ),
@@ -559,15 +540,15 @@ class MockCalendricalEvent extends _i1.Mock implements _i13.CalendricalEvent {
         returnValueForMissingStub: <String, dynamic>{},
       ) as Map<String, dynamic>);
   @override
-  _i13.CalendricalEvent copyWith({
+  _i12.CalendricalEvent copyWith({
     String? eventID,
     String? groupID,
     String? authorID,
-    _i17.GroupType? groupType,
-    _i9.CalendricalEventType? eventType,
-    _i10.Date? date,
-    _i11.Time? startTime,
-    _i11.Time? endTime,
+    _i16.GroupType? groupType,
+    _i12.EventType? eventType,
+    _i9.Date? date,
+    _i10.Time? startTime,
+    _i10.Time? endTime,
     String? title,
     String? detail,
     String? place,
@@ -594,7 +575,7 @@ class MockCalendricalEvent extends _i1.Mock implements _i13.CalendricalEvent {
             #latestEditor: latestEditor,
           },
         ),
-        returnValue: _FakeCalendricalEvent_12(
+        returnValue: _FakeCalendricalEvent_11(
           this,
           Invocation.method(
             #copyWith,
@@ -616,7 +597,7 @@ class MockCalendricalEvent extends _i1.Mock implements _i13.CalendricalEvent {
             },
           ),
         ),
-        returnValueForMissingStub: _FakeCalendricalEvent_12(
+        returnValueForMissingStub: _FakeCalendricalEvent_11(
           this,
           Invocation.method(
             #copyWith,
@@ -638,5 +619,5 @@ class MockCalendricalEvent extends _i1.Mock implements _i13.CalendricalEvent {
             },
           ),
         ),
-      ) as _i13.CalendricalEvent);
+      ) as _i12.CalendricalEvent);
 }
diff --git a/app/test_goldens/dashboard/dashboard_page_test.dart b/app/test_goldens/dashboard/dashboard_page_test.dart
index 87bb96918..5b1612e96 100644
--- a/app/test_goldens/dashboard/dashboard_page_test.dart
+++ b/app/test_goldens/dashboard/dashboard_page_test.dart
@@ -10,13 +10,14 @@ import 'dart:async';
 import 'dart:convert';
 
 import 'package:bloc_provider/bloc_provider.dart';
+import 'package:clock/clock.dart';
 import 'package:flutter/material.dart';
 import 'package:flutter_test/flutter_test.dart';
 import 'package:golden_toolkit/golden_toolkit.dart';
 import 'package:holidays/holidays.dart';
 import 'package:intl/intl.dart';
-import 'package:sharezone/holidays/holiday_bloc.dart';
 import 'package:sharezone/dashboard/dashboard_page.dart';
+import 'package:sharezone/holidays/holiday_bloc.dart';
 import 'package:sharezone_widgets/sharezone_widgets.dart';
 
 class FakeHolidayBloc extends Fake implements HolidayBloc {
@@ -42,7 +43,7 @@ void main() {
       final holidayBloc = FakeHolidayBloc();
       addTearDown(holidayBloc.dispose);
 
-      final now = DateTime.now();
+      final now = clock.now();
       final firstHolidays = Holiday.fromJson(jsonEncode({
         "start": DateFormat('yyyy-MM-dd').format(now),
         "end": "${now.year + 1}-02-01",
diff --git a/lib/abgabe/abgabe_client_lib/lib/src/erstellung/bloc/homework_user_create_submissions_bloc_factory.dart b/lib/abgabe/abgabe_client_lib/lib/src/erstellung/bloc/homework_user_create_submissions_bloc_factory.dart
index a84c59a35..31ce580f8 100644
--- a/lib/abgabe/abgabe_client_lib/lib/src/erstellung/bloc/homework_user_create_submissions_bloc_factory.dart
+++ b/lib/abgabe/abgabe_client_lib/lib/src/erstellung/bloc/homework_user_create_submissions_bloc_factory.dart
@@ -16,6 +16,7 @@ import 'package:abgabe_client_lib/src/erstellung/use_cases/datei_loescher.dart';
 import 'package:abgabe_client_lib/src/erstellung/use_cases/datei_umbenenner.dart';
 import 'package:abgabe_http_api/api.dart';
 import 'package:bloc_base/bloc_base.dart';
+import 'package:clock/clock.dart';
 import 'package:common_domain_models/common_domain_models.dart';
 
 class HomeworkUserCreateSubmissionsBlocFactory extends BlocBase {
@@ -59,7 +60,7 @@ class HomeworkUserCreateSubmissionsBlocFactory extends BlocBase {
       umbenenner,
       veroeffentlicher,
       gateway.streamAbgabezeitpunktFuerHausaufgabe(id),
-      () => DateTime.now(),
+      () => clock.now(),
     );
   }
 
diff --git a/lib/abgabe/abgabe_client_lib/lib/src/erstellung/cloud_storage_abgabedatei_uploader.dart b/lib/abgabe/abgabe_client_lib/lib/src/erstellung/cloud_storage_abgabedatei_uploader.dart
index 82f0f8914..fda44a91c 100644
--- a/lib/abgabe/abgabe_client_lib/lib/src/erstellung/cloud_storage_abgabedatei_uploader.dart
+++ b/lib/abgabe/abgabe_client_lib/lib/src/erstellung/cloud_storage_abgabedatei_uploader.dart
@@ -12,7 +12,7 @@ import 'package:abgabe_client_lib/src/erstellung/datei_upload_prozess.dart';
 import 'package:abgabe_client_lib/src/erstellung/local_file_saver.dart';
 import 'package:abgabe_client_lib/src/models/models.dart';
 import 'package:abgabe_http_api/api/abgabedatei_api.dart';
-
+import 'package:clock/clock.dart';
 import 'package:crash_analytics/crash_analytics.dart';
 import 'package:files_basics/local_file.dart';
 import 'package:filesharing_logic/file_uploader.dart';
@@ -20,7 +20,7 @@ import 'package:filesharing_logic/file_uploader.dart';
 import 'uploader/abgabedatei_uploader.dart';
 import 'use_cases/abgabedatei_hinzufueger.dart';
 
-DateTime _lastUploaded = DateTime.now();
+DateTime _lastUploaded = clock.now();
 
 class CloudStorageAbgabedateiUploader extends AbgabedateiUploader {
   final FileUploader fileUploader;
@@ -57,11 +57,11 @@ class CloudStorageAbgabedateiUploader extends AbgabedateiUploader {
           /// passieren kann, dass das hinzufügen einer Datei "überschrieben"
           /// also sozusagen rückgängig gemacht wird, wenn die Anfragen parallel
           /// verarbeitet werden.
-          while (DateTime.now().difference(_lastUploaded).abs() <
+          while (clock.now().difference(_lastUploaded).abs() <
               const Duration(milliseconds: 900)) {
             await Future.delayed(const Duration(milliseconds: 300));
           }
-          _lastUploaded = DateTime.now();
+          _lastUploaded = clock.now();
           await _fuegeAbgabedateireferenzZuAbgabeHinzu(befehl);
         } catch (e, s) {
           await _logAbgabedateireferenzHinzufuegeError(e, s);
diff --git a/lib/abgabe/abgabe_client_lib/pubspec.lock b/lib/abgabe/abgabe_client_lib/pubspec.lock
index cd73207ed..da2893ade 100644
--- a/lib/abgabe/abgabe_client_lib/pubspec.lock
+++ b/lib/abgabe/abgabe_client_lib/pubspec.lock
@@ -142,7 +142,7 @@ packages:
     source: hosted
     version: "1.7.0"
   clock:
-    dependency: transitive
+    dependency: "direct main"
     description:
       name: clock
       sha256: cb6d7f03e1de671e34607e909a7213e31d7752be4fb66a86d29fe1eb14bfb5cf
diff --git a/lib/abgabe/abgabe_client_lib/pubspec.yaml b/lib/abgabe/abgabe_client_lib/pubspec.yaml
index 81772cf59..090c7ea31 100644
--- a/lib/abgabe/abgabe_client_lib/pubspec.yaml
+++ b/lib/abgabe/abgabe_client_lib/pubspec.yaml
@@ -39,6 +39,7 @@ dependencies:
   meta: ^1.1.8
   rxdart: ^0.27.1
   collection: ^1.17.2
+  clock: ^1.1.1
 
 dev_dependencies:
   flutter_test:
diff --git a/lib/abgabe/abgabe_client_lib/test/bloc_test.dart b/lib/abgabe/abgabe_client_lib/test/bloc_test.dart
index e44629070..c7724e5a2 100644
--- a/lib/abgabe/abgabe_client_lib/test/bloc_test.dart
+++ b/lib/abgabe/abgabe_client_lib/test/bloc_test.dart
@@ -19,15 +19,14 @@ import 'package:abgabe_client_lib/src/erstellung/use_cases/datei_loescher.dart';
 import 'package:abgabe_client_lib/src/erstellung/use_cases/datei_umbenenner.dart';
 import 'package:abgabe_client_lib/src/erstellung/views.dart';
 import 'package:abgabe_client_lib/src/models/models.dart';
-
 import 'package:async/async.dart';
+import 'package:clock/clock.dart';
 import 'package:common_domain_models/common_domain_models.dart';
 import 'package:files_basics/files_models.dart';
 import 'package:files_basics/local_file.dart';
-
-import 'package:test_randomness/test_randomness.dart';
-import 'package:rxdart/subjects.dart';
 import 'package:flutter_test/flutter_test.dart';
+import 'package:rxdart/subjects.dart';
+import 'package:test_randomness/test_randomness.dart';
 
 void main() {
   group(
@@ -753,9 +752,9 @@ void main() {
         });
 
         test('Die Dateien werden nach hinzufuegedatum sortiert.', () async {
-          final now = DateTime.now();
+          final now = clock.now();
           abgabezeitpunktStream.add(now.add(const Duration(days: 20)));
-          kriegeAktuelleZeit = () => DateTime.now();
+          kriegeAktuelleZeit = () => clock.now();
 
           useCases.abgabe.add(
               erstelleAbgabenModelSnapshot(abgegeben: false, abgabedateien: [
@@ -853,7 +852,7 @@ HochgeladeneAbgabedatei hochgeladeneAbgabedatei({
     groesse: Dateigroesse(12345),
     downloadUrl: DateiDownloadUrl('https://some-url.com'),
     // Sollte letzte sein (auch wenn es eigentlich nicht sein)
-    erstellungsdatum: erstellungsdatum ?? DateTime.now(),
+    erstellungsdatum: erstellungsdatum ?? clock.now(),
   );
 }
 
@@ -864,7 +863,7 @@ ErstellerAbgabeModelSnapshot erstelleAbgabenModelSnapshot(
           abgabeId: AbgabeId(
               AbgabezielId.homework(HomeworkId('ValidHomeworkId')),
               UserId('ValidUserId')),
-          abgegebenUm: abgegeben ? DateTime.now() : null,
+          abgegebenUm: abgegeben ? clock.now() : null,
           abgabedateien: abgabedateien)
       .toSnapshot();
 }
diff --git a/lib/authentification/authentification_qrcode/lib/src/logic/qr_code_user_authenticator.dart b/lib/authentification/authentification_qrcode/lib/src/logic/qr_code_user_authenticator.dart
index b0b311c50..5c1e513e9 100644
--- a/lib/authentification/authentification_qrcode/lib/src/logic/qr_code_user_authenticator.dart
+++ b/lib/authentification/authentification_qrcode/lib/src/logic/qr_code_user_authenticator.dart
@@ -7,7 +7,9 @@
 // SPDX-License-Identifier: EUPL-1.2
 
 import 'package:app_functions/sharezone_app_functions.dart';
+import 'package:clock/clock.dart';
 import 'package:cloud_firestore/cloud_firestore.dart';
+
 import '../models/qr_sign_in_document.dart';
 import '../models/qr_sign_in_state.dart';
 
@@ -48,7 +50,7 @@ class QrCodeUserAuthenticator {
     final qrSignInDocument = QrSignInDocument(
       qrId: qrId,
       publicKey: publicKey,
-      created: DateTime.now(),
+      created: clock.now(),
     );
     _qrSignInCollection.doc(qrId).set(qrSignInDocument.toData());
     return qrId;
diff --git a/lib/authentification/authentification_qrcode/pubspec.lock b/lib/authentification/authentification_qrcode/pubspec.lock
index 6d85126eb..7bcf2d604 100644
--- a/lib/authentification/authentification_qrcode/pubspec.lock
+++ b/lib/authentification/authentification_qrcode/pubspec.lock
@@ -101,7 +101,7 @@ packages:
     source: hosted
     version: "1.3.0"
   clock:
-    dependency: transitive
+    dependency: "direct main"
     description:
       name: clock
       sha256: cb6d7f03e1de671e34607e909a7213e31d7752be4fb66a86d29fe1eb14bfb5cf
diff --git a/lib/authentification/authentification_qrcode/pubspec.yaml b/lib/authentification/authentification_qrcode/pubspec.yaml
index 7c0883ec7..7373cdd09 100644
--- a/lib/authentification/authentification_qrcode/pubspec.yaml
+++ b/lib/authentification/authentification_qrcode/pubspec.yaml
@@ -35,6 +35,7 @@ dependencies:
   fast_rsa: ^3.6.1
   firebase_auth: ^4.7.3
   rxdart: ^0.27.1
+  clock: ^1.1.1
 
 dev_dependencies:
   flutter_test:
diff --git a/lib/cloud_firestore_helper/lib/src/cloud_firestore_helper.dart b/lib/cloud_firestore_helper/lib/src/cloud_firestore_helper.dart
index d8d6b968a..8e8c3ca27 100644
--- a/lib/cloud_firestore_helper/lib/src/cloud_firestore_helper.dart
+++ b/lib/cloud_firestore_helper/lib/src/cloud_firestore_helper.dart
@@ -6,6 +6,8 @@
 //
 // SPDX-License-Identifier: EUPL-1.2
 
+import 'package:clock/clock.dart';
+
 typedef ObjectMapBuilder<T> = T Function(String key, dynamic decodedMapValue);
 typedef ObjectListBuilder<T> = T Function(dynamic decodedMapValue);
 
@@ -42,7 +44,7 @@ List<T> decodeList<T>(dynamic data, ObjectListBuilder<T> builder) {
 /// behavior is legacy and shouldn't be used anymore.
 DateTime dateTimeFromTimestamp(dynamic timestamp) {
   final dateTime = dateTimeFromTimestampOrNull(timestamp);
-  return dateTime ?? DateTime.now();
+  return dateTime ?? clock.now();
 }
 
 DateTime? dateTimeFromTimestampOrNull(dynamic timestamp) {
diff --git a/lib/cloud_firestore_helper/pubspec.lock b/lib/cloud_firestore_helper/pubspec.lock
index 60a125941..b1201c533 100644
--- a/lib/cloud_firestore_helper/pubspec.lock
+++ b/lib/cloud_firestore_helper/pubspec.lock
@@ -1,6 +1,14 @@
 # Generated by pub
 # See https://dart.dev/tools/pub/glossary#lockfile
 packages:
+  clock:
+    dependency: "direct main"
+    description:
+      name: clock
+      sha256: cb6d7f03e1de671e34607e909a7213e31d7752be4fb66a86d29fe1eb14bfb5cf
+      url: "https://pub.dev"
+    source: hosted
+    version: "1.1.1"
   flutter_lints:
     dependency: transitive
     description:
diff --git a/lib/cloud_firestore_helper/pubspec.yaml b/lib/cloud_firestore_helper/pubspec.yaml
index 266976927..b46649772 100644
--- a/lib/cloud_firestore_helper/pubspec.yaml
+++ b/lib/cloud_firestore_helper/pubspec.yaml
@@ -20,3 +20,6 @@ environment:
 dev_dependencies:
   sharezone_lints:
     path: ../sharezone_lints
+    
+dependencies:
+  clock: ^1.1.1
diff --git a/lib/date/lib/src/date.dart b/lib/date/lib/src/date.dart
index f782ed740..664a4f00f 100644
--- a/lib/date/lib/src/date.dart
+++ b/lib/date/lib/src/date.dart
@@ -6,7 +6,9 @@
 //
 // SPDX-License-Identifier: EUPL-1.2
 
+import 'package:clock/clock.dart';
 import 'package:intl/intl.dart';
+
 import 'weekday.dart';
 
 class Date {
@@ -31,7 +33,7 @@ class Date {
     return Date._(dateTime.toIso8601String().substring(0, 10));
   }
 
-  factory Date.today() => Date.fromDateTime(DateTime.now());
+  factory Date.today() => Date.fromDateTime(clock.now());
 
   /// Gibt das aktuelle [Date] als Stream zurück.
   ///
diff --git a/lib/date/pubspec.lock b/lib/date/pubspec.lock
index ae3524d2f..e6e271e78 100644
--- a/lib/date/pubspec.lock
+++ b/lib/date/pubspec.lock
@@ -10,7 +10,7 @@ packages:
     source: hosted
     version: "1.3.0"
   clock:
-    dependency: transitive
+    dependency: "direct main"
     description:
       name: clock
       sha256: cb6d7f03e1de671e34607e909a7213e31d7752be4fb66a86d29fe1eb14bfb5cf
diff --git a/lib/date/pubspec.yaml b/lib/date/pubspec.yaml
index d2e193fd2..020f1fc04 100644
--- a/lib/date/pubspec.yaml
+++ b/lib/date/pubspec.yaml
@@ -19,6 +19,7 @@ dependencies:
   rxdart: ^0.27.1
   flutter:
     sdk: flutter
+  clock: ^1.1.1
 
 dev_dependencies:
   sharezone_lints:
diff --git a/lib/filesharing/filesharing_logic/lib/src/models/cloud_file.dart b/lib/filesharing/filesharing_logic/lib/src/models/cloud_file.dart
index ae1416d05..a9f8217eb 100644
--- a/lib/filesharing/filesharing_logic/lib/src/models/cloud_file.dart
+++ b/lib/filesharing/filesharing_logic/lib/src/models/cloud_file.dart
@@ -6,9 +6,10 @@
 //
 // SPDX-License-Identifier: EUPL-1.2
 
+import 'package:clock/clock.dart';
 import 'package:cloud_firestore/cloud_firestore.dart';
-import 'package:files_basics/files_models.dart';
 import 'package:cloud_firestore_helper/cloud_firestore_helper.dart';
+import 'package:files_basics/files_models.dart';
 
 import 'change_activity.dart';
 import 'folder_path.dart';
@@ -83,7 +84,7 @@ class CloudFile {
       name: '',
       downloadURL: null,
       thumbnailURL: null,
-      createdOn: DateTime.now(),
+      createdOn: clock.now(),
       sizeBytes: null,
       fileFormat: FileFormat.unknown,
       forUsers: {},
diff --git a/lib/filesharing/filesharing_logic/pubspec.lock b/lib/filesharing/filesharing_logic/pubspec.lock
index 6a09a158d..730287124 100644
--- a/lib/filesharing/filesharing_logic/pubspec.lock
+++ b/lib/filesharing/filesharing_logic/pubspec.lock
@@ -64,7 +64,7 @@ packages:
     source: hosted
     version: "1.7.0"
   clock:
-    dependency: transitive
+    dependency: "direct main"
     description:
       name: clock
       sha256: cb6d7f03e1de671e34607e909a7213e31d7752be4fb66a86d29fe1eb14bfb5cf
diff --git a/lib/filesharing/filesharing_logic/pubspec.yaml b/lib/filesharing/filesharing_logic/pubspec.yaml
index 6dd03310f..97a6c03fc 100644
--- a/lib/filesharing/filesharing_logic/pubspec.yaml
+++ b/lib/filesharing/filesharing_logic/pubspec.yaml
@@ -33,6 +33,7 @@ dependencies:
   permission_handler: ^11.1.0
   helper_functions:
     path: ../../helper_functions
+  clock: ^1.1.1
 
 dev_dependencies:
   flutter_test:
diff --git a/lib/firebase_hausaufgabenheft_logik/lib/src/homework_dto.dart b/lib/firebase_hausaufgabenheft_logik/lib/src/homework_dto.dart
index f36ba3d13..aba542866 100644
--- a/lib/firebase_hausaufgabenheft_logik/lib/src/homework_dto.dart
+++ b/lib/firebase_hausaufgabenheft_logik/lib/src/homework_dto.dart
@@ -6,9 +6,10 @@
 //
 // SPDX-License-Identifier: EUPL-1.2
 
+import 'package:clock/clock.dart';
 import 'package:cloud_firestore/cloud_firestore.dart';
-import 'package:collection/collection.dart';
 import 'package:cloud_firestore_helper/cloud_firestore_helper.dart';
+import 'package:collection/collection.dart';
 
 class HomeworkDto {
   final String id;
@@ -128,7 +129,7 @@ class HomeworkDto {
       description: "",
       withSubmissions: false,
       submitters: [],
-      todoUntil: DateTime.now(),
+      todoUntil: clock.now(),
       createdOn: null,
       attachments: [],
       private: false,
diff --git a/lib/firebase_hausaufgabenheft_logik/pubspec.lock b/lib/firebase_hausaufgabenheft_logik/pubspec.lock
index baadf80a5..75545d957 100644
--- a/lib/firebase_hausaufgabenheft_logik/pubspec.lock
+++ b/lib/firebase_hausaufgabenheft_logik/pubspec.lock
@@ -65,7 +65,7 @@ packages:
     source: hosted
     version: "1.3.0"
   clock:
-    dependency: transitive
+    dependency: "direct main"
     description:
       name: clock
       sha256: cb6d7f03e1de671e34607e909a7213e31d7752be4fb66a86d29fe1eb14bfb5cf
diff --git a/lib/firebase_hausaufgabenheft_logik/pubspec.yaml b/lib/firebase_hausaufgabenheft_logik/pubspec.yaml
index 4d7832a02..5fc1a355b 100644
--- a/lib/firebase_hausaufgabenheft_logik/pubspec.yaml
+++ b/lib/firebase_hausaufgabenheft_logik/pubspec.yaml
@@ -27,6 +27,7 @@ dependencies:
   cloud_firestore: ^4.8.5
   flutter:
     sdk: flutter
+  clock: ^1.1.1
 
 dev_dependencies:
   rxdart: ^0.27.1
diff --git a/lib/firebase_hausaufgabenheft_logik/test/lazy_loading_controller_test.dart b/lib/firebase_hausaufgabenheft_logik/test/lazy_loading_controller_test.dart
index bec652661..11c176af8 100644
--- a/lib/firebase_hausaufgabenheft_logik/test/lazy_loading_controller_test.dart
+++ b/lib/firebase_hausaufgabenheft_logik/test/lazy_loading_controller_test.dart
@@ -8,11 +8,13 @@
 
 import 'dart:async';
 
+import 'package:clock/clock.dart';
 import 'package:common_domain_models/common_domain_models.dart';
 import 'package:firebase_hausaufgabenheft_logik/src/realtime_updating_lazy_loading_controller.dart';
 import 'package:flutter_test/flutter_test.dart';
-import 'package:rxdart/subjects.dart' as rx;
 import 'package:hausaufgabenheft_logik/hausaufgabenheft_logik.dart';
+import 'package:rxdart/subjects.dart' as rx;
+
 import 'in_memory_homework_loader.dart';
 
 class ReportingInMemoryHomeworkLoader extends InMemoryHomeworkLoader {
@@ -31,7 +33,7 @@ List<HomeworkReadModel> listOfHomeworksWithLength(int length) => List.generate(
       length,
       (index) => HomeworkReadModel(
           id: HomeworkId("$index"),
-          todoDate: DateTime.now(),
+          todoDate: clock.now(),
           status: CompletionStatus.completed,
           subject: Subject("Mathe", abbreviation: 'Ma'),
           title: const Title("ABC"),
diff --git a/lib/group_domain_models/lib/src/models/member.dart b/lib/group_domain_models/lib/src/models/member.dart
index 4474fbeb5..b848a23a5 100644
--- a/lib/group_domain_models/lib/src/models/member.dart
+++ b/lib/group_domain_models/lib/src/models/member.dart
@@ -6,9 +6,10 @@
 //
 // SPDX-License-Identifier: EUPL-1.2
 
+import 'package:clock/clock.dart';
+import 'package:cloud_firestore_helper/cloud_firestore_helper.dart';
 import 'package:common_domain_models/common_domain_models.dart';
 import 'package:flutter/foundation.dart';
-import 'package:cloud_firestore_helper/cloud_firestore_helper.dart';
 import 'package:user/user.dart';
 
 import 'member_role.dart';
@@ -41,7 +42,7 @@ class MemberData {
       abbreviation: generateAbbreviation(user.name),
       role: role,
       typeOfUser: user.typeOfUser,
-      joinedOn: DateTime.now(),
+      joinedOn: clock.now(),
     );
   }
 
diff --git a/lib/group_domain_models/pubspec.lock b/lib/group_domain_models/pubspec.lock
index 74dbd539f..011f5c53f 100644
--- a/lib/group_domain_models/pubspec.lock
+++ b/lib/group_domain_models/pubspec.lock
@@ -64,7 +64,7 @@ packages:
     source: hosted
     version: "1.3.0"
   clock:
-    dependency: transitive
+    dependency: "direct main"
     description:
       name: clock
       sha256: cb6d7f03e1de671e34607e909a7213e31d7752be4fb66a86d29fe1eb14bfb5cf
diff --git a/lib/group_domain_models/pubspec.yaml b/lib/group_domain_models/pubspec.yaml
index 212775cd9..ce2748f3c 100644
--- a/lib/group_domain_models/pubspec.yaml
+++ b/lib/group_domain_models/pubspec.yaml
@@ -27,6 +27,7 @@ dependencies:
     path: ../design
   flutter:
     sdk: flutter
+  clock: ^1.1.1
 
 dev_dependencies:
   flutter_test:
diff --git a/lib/hausaufgabenheft_logik/lib/src/models/date.dart b/lib/hausaufgabenheft_logik/lib/src/models/date.dart
index 91730749b..d0f1896e6 100644
--- a/lib/hausaufgabenheft_logik/lib/src/models/date.dart
+++ b/lib/hausaufgabenheft_logik/lib/src/models/date.dart
@@ -6,6 +6,8 @@
 //
 // SPDX-License-Identifier: EUPL-1.2
 
+import 'package:clock/clock.dart';
+
 class Date implements Comparable<Date> {
   final int day;
   final int month;
@@ -18,7 +20,7 @@ class Date implements Comparable<Date> {
   });
 
   factory Date.now() {
-    final now = DateTime.now();
+    final now = clock.now();
     return Date(day: now.day, month: now.month, year: now.year);
   }
 
diff --git a/lib/hausaufgabenheft_logik/lib/src/setup/create_homework_page_bloc.dart b/lib/hausaufgabenheft_logik/lib/src/setup/create_homework_page_bloc.dart
index a4a61d01f..cfac84e32 100644
--- a/lib/hausaufgabenheft_logik/lib/src/setup/create_homework_page_bloc.dart
+++ b/lib/hausaufgabenheft_logik/lib/src/setup/create_homework_page_bloc.dart
@@ -6,19 +6,20 @@
 //
 // SPDX-License-Identifier: EUPL-1.2
 
+import 'package:clock/clock.dart';
 import 'package:hausaufgabenheft_logik/src/homework_completion/homework_page_completion_dispatcher.dart';
-import 'package:hausaufgabenheft_logik/src/student_homework_page_bloc/homework_sorting_cache.dart';
 import 'package:hausaufgabenheft_logik/src/open_homeworks/open_homework_list_bloc/open_homework_list_bloc.dart';
 import 'package:hausaufgabenheft_logik/src/open_homeworks/open_homework_view_bloc/open_homework_view_bloc.dart';
+import 'package:hausaufgabenheft_logik/src/student_homework_page_bloc/homework_sorting_cache.dart';
 
 import '../completed_homeworks/completed_homeworks_view_bloc/completed_homeworks_view_bloc.dart';
 import '../completed_homeworks/lazy_loading_completed_homeworks_bloc/lazy_loading_completed_homeworks_bloc.dart';
 import '../completed_homeworks/views/completed_homework_list_view_factory.dart';
-import '../student_homework_page_bloc/student_homework_page_bloc.dart';
 import '../models/homework/models_used_by_homework.dart';
 import '../open_homeworks/sort_and_subcategorization/sort_and_subcategorizer.dart';
 import '../open_homeworks/sort_and_subcategorization/subcategorizer_factory.dart';
 import '../open_homeworks/views/open_homework_list_view_factory.dart';
+import '../student_homework_page_bloc/student_homework_page_bloc.dart';
 import '../views/student_homework_view_factory.dart';
 import 'config.dart';
 import 'dependencies.dart';
@@ -54,6 +55,6 @@ HomeworkPageBloc createHomeworkPageBloc(
     completedHomeworksViewBloc: completedHomeworksViewBloc,
     homeworkCompletionReceiver: homeworkPageCompletionReceiver,
     homeworkSortingCache: HomeworkSortingCache(dependencies.keyValueStore),
-    getCurrentDateTime: dependencies.getCurrentDateTime ?? () => DateTime.now(),
+    getCurrentDateTime: dependencies.getCurrentDateTime ?? () => clock.now(),
   );
 }
diff --git a/lib/hausaufgabenheft_logik/pubspec.lock b/lib/hausaufgabenheft_logik/pubspec.lock
index bbf0aabd0..af545a917 100644
--- a/lib/hausaufgabenheft_logik/pubspec.lock
+++ b/lib/hausaufgabenheft_logik/pubspec.lock
@@ -65,7 +65,7 @@ packages:
     source: hosted
     version: "2.1.1"
   clock:
-    dependency: transitive
+    dependency: "direct main"
     description:
       name: clock
       sha256: cb6d7f03e1de671e34607e909a7213e31d7752be4fb66a86d29fe1eb14bfb5cf
diff --git a/lib/hausaufgabenheft_logik/pubspec.yaml b/lib/hausaufgabenheft_logik/pubspec.yaml
index e4584efb8..a39969ea1 100644
--- a/lib/hausaufgabenheft_logik/pubspec.yaml
+++ b/lib/hausaufgabenheft_logik/pubspec.yaml
@@ -30,6 +30,7 @@ dependencies:
   # https://gitlab.com/codingbrain/sharezone/sharezone-app/-/issues/1460
   test_randomness:
     path: ../test_randomness
+  clock: ^1.1.1
 
 dev_dependencies:
   async: ^2.11.0
diff --git a/lib/hausaufgabenheft_logik/test/date/date_test.dart b/lib/hausaufgabenheft_logik/test/date/date_test.dart
index 3b5751b71..f1b3db911 100644
--- a/lib/hausaufgabenheft_logik/test/date/date_test.dart
+++ b/lib/hausaufgabenheft_logik/test/date/date_test.dart
@@ -6,6 +6,7 @@
 //
 // SPDX-License-Identifier: EUPL-1.2
 
+import 'package:clock/clock.dart';
 import 'package:hausaufgabenheft_logik/src/models/date.dart';
 import 'package:test/test.dart';
 
@@ -50,7 +51,7 @@ void main() {
 
     test('Date.now', () {
       final now = Date.now();
-      var nowDateTime = DateTime.now();
+      var nowDateTime = clock.now();
       expect(now.year, nowDateTime.year);
       expect(now.month, nowDateTime.month);
       expect(now.day, nowDateTime.day);
diff --git a/lib/hausaufgabenheft_logik/test/homework_page_bloc_test.dart b/lib/hausaufgabenheft_logik/test/homework_page_bloc_test.dart
index 815ce3a43..a1652b449 100644
--- a/lib/hausaufgabenheft_logik/test/homework_page_bloc_test.dart
+++ b/lib/hausaufgabenheft_logik/test/homework_page_bloc_test.dart
@@ -10,6 +10,7 @@ import 'dart:async';
 import 'dart:developer';
 
 import 'package:bloc/bloc.dart';
+import 'package:clock/clock.dart';
 import 'package:hausaufgabenheft_logik/hausaufgabenheft_logik.dart';
 import 'package:hausaufgabenheft_logik/hausaufgabenheft_logik_setup.dart';
 import 'package:hausaufgabenheft_logik/src/completed_homeworks/completed_homeworks_view_bloc/completed_homeworks_view_bloc.dart'
@@ -338,7 +339,7 @@ void main() {
         'should show dialog to check all completed homework when more than 2 open overdue homeworks',
         () async {
       final yesterday =
-          Date.fromDateTime(DateTime.now().subtract(const Duration(days: 1)));
+          Date.fromDateTime(clock.now().subtract(const Duration(days: 1)));
       final homeworks = List.generate(
           3, (_) => createHomework(done: false, todoDate: yesterday));
 
@@ -352,9 +353,9 @@ void main() {
         'does not show dialog to check all completed homework with less than 3 overdue homeworks',
         () async {
       final yesterday =
-          Date.fromDateTime(DateTime.now().subtract(const Duration(days: 1)));
+          Date.fromDateTime(clock.now().subtract(const Duration(days: 1)));
       final tomorrow =
-          Date.fromDateTime(DateTime.now().add(const Duration(days: 1)));
+          Date.fromDateTime(clock.now().add(const Duration(days: 1)));
 
       final homeworks = [
         ...List.generate(
diff --git a/lib/holidays/lib/src/holiday_cache.dart b/lib/holidays/lib/src/holiday_cache.dart
index 853536a46..f2c1e159f 100644
--- a/lib/holidays/lib/src/holiday_cache.dart
+++ b/lib/holidays/lib/src/holiday_cache.dart
@@ -7,7 +7,9 @@
 // SPDX-License-Identifier: EUPL-1.2
 
 import 'package:built_collection/built_collection.dart';
+import 'package:clock/clock.dart';
 import 'package:key_value_store/key_value_store.dart';
+
 import 'api/holiday.dart';
 import 'state.dart';
 
@@ -21,7 +23,7 @@ class HolidayCache {
   HolidayCache(this.cache,
       {this.maxValidDurationTillLastSaved = const Duration(days: 30),
       this.getCurrentTime}) {
-    getCurrentTime ??= () => DateTime.now();
+    getCurrentTime ??= () => clock.now();
   }
 
   CacheResponse? load(State state) {
diff --git a/lib/holidays/pubspec.lock b/lib/holidays/pubspec.lock
index 87635c68d..1c7332ce7 100644
--- a/lib/holidays/pubspec.lock
+++ b/lib/holidays/pubspec.lock
@@ -144,7 +144,7 @@ packages:
     source: hosted
     version: "2.0.3"
   clock:
-    dependency: transitive
+    dependency: "direct main"
     description:
       name: clock
       sha256: cb6d7f03e1de671e34607e909a7213e31d7752be4fb66a86d29fe1eb14bfb5cf
diff --git a/lib/holidays/pubspec.yaml b/lib/holidays/pubspec.yaml
index c0fd2c953..3a806cd80 100644
--- a/lib/holidays/pubspec.yaml
+++ b/lib/holidays/pubspec.yaml
@@ -23,6 +23,7 @@ dependencies:
   cloud_functions: ^4.4.0
   app_functions:
     path: ../app_functions
+  clock: ^1.1.1
 
 dev_dependencies:
   # We need to add the `flutter` package as dev dependency as workaround for the
diff --git a/lib/sharezone_widgets/lib/src/widgets.dart b/lib/sharezone_widgets/lib/src/widgets.dart
index 8e014cae1..630708dc5 100644
--- a/lib/sharezone_widgets/lib/src/widgets.dart
+++ b/lib/sharezone_widgets/lib/src/widgets.dart
@@ -9,9 +9,10 @@
 import 'dart:async';
 import 'dart:developer';
 
+import 'package:clock/clock.dart';
 import 'package:flutter/material.dart';
-import 'package:intl/intl.dart';
 import 'package:helper_functions/helper_functions.dart';
+import 'package:intl/intl.dart';
 import 'package:sharezone_widgets/sharezone_widgets.dart';
 
 export 'prefilled_text_field.dart';
@@ -66,7 +67,7 @@ class DatePicker extends StatelessWidget {
   Future<void> _selectDate(BuildContext context) async {
     FocusManager.instance.primaryFocus?.unfocus();
     final DateTime tomorrow =
-        DateTime(DateTime.now().year, DateTime.now().month, DateTime.now().day)
+        DateTime(clock.now().year, clock.now().month, clock.now().day)
             .add(const Duration(days: 1));
     final DateTime? picked = await showDatePicker(
       context: context,
diff --git a/lib/sharezone_widgets/pubspec.lock b/lib/sharezone_widgets/pubspec.lock
index 9ec132a39..7bfe6c06c 100644
--- a/lib/sharezone_widgets/pubspec.lock
+++ b/lib/sharezone_widgets/pubspec.lock
@@ -41,7 +41,7 @@ packages:
     source: hosted
     version: "1.3.0"
   clock:
-    dependency: transitive
+    dependency: "direct main"
     description:
       name: clock
       sha256: cb6d7f03e1de671e34607e909a7213e31d7752be4fb66a86d29fe1eb14bfb5cf
diff --git a/lib/sharezone_widgets/pubspec.yaml b/lib/sharezone_widgets/pubspec.yaml
index 554673a67..07f19a6d3 100644
--- a/lib/sharezone_widgets/pubspec.yaml
+++ b/lib/sharezone_widgets/pubspec.yaml
@@ -29,6 +29,7 @@ dependencies:
   rxdart: ^0.27.1
   flutter:
     sdk: flutter
+  clock: ^1.1.1
 
 dev_dependencies:
   flutter_test:
diff --git a/tools/sz_repo_cli/lib/src/common/src/concurrent_command.dart b/tools/sz_repo_cli/lib/src/common/src/concurrent_command.dart
index a0151f3eb..541d78d0d 100644
--- a/tools/sz_repo_cli/lib/src/common/src/concurrent_command.dart
+++ b/tools/sz_repo_cli/lib/src/common/src/concurrent_command.dart
@@ -9,6 +9,7 @@
 import 'dart:async';
 import 'dart:io';
 
+import 'package:clock/clock.dart';
 import 'package:sz_repo_cli/src/common/common.dart';
 
 /// Run a task via [runTaskForPackage] for many [Package] concurrently.
@@ -91,7 +92,7 @@ abstract class ConcurrentCommand extends CommandBase {
         : null;
 
     final taskRunner = ConcurrentPackageTaskRunner(
-      getCurrentDateTime: () => DateTime.now(),
+      getCurrentDateTime: () => clock.now(),
     );
 
     final res = taskRunner
diff --git a/tools/sz_repo_cli/lib/src/common/src/concurrent_package_task_runner.dart b/tools/sz_repo_cli/lib/src/common/src/concurrent_package_task_runner.dart
index 5a647a8cb..5f651cd1d 100644
--- a/tools/sz_repo_cli/lib/src/common/src/concurrent_package_task_runner.dart
+++ b/tools/sz_repo_cli/lib/src/common/src/concurrent_package_task_runner.dart
@@ -10,6 +10,7 @@ import 'dart:async';
 import 'dart:collection';
 import 'dart:io';
 
+import 'package:clock/clock.dart';
 import 'package:rxdart/subjects.dart';
 import 'package:rxdart/transformers.dart';
 import 'package:sz_repo_cli/src/common/common.dart';
@@ -20,7 +21,7 @@ class ConcurrentPackageTaskRunner {
   ConcurrentPackageTaskRunner({
     DateTime Function()? getCurrentDateTime,
   }) {
-    _getCurrentDateTime = getCurrentDateTime ?? () => DateTime.now();
+    _getCurrentDateTime = getCurrentDateTime ?? () => clock.now();
   }
 
   /// Run [runTask] for every [Package] emitted by the [packageStream].
diff --git a/tools/sz_repo_cli/pubspec.lock b/tools/sz_repo_cli/pubspec.lock
index c7019dd11..fc669c965 100644
--- a/tools/sz_repo_cli/pubspec.lock
+++ b/tools/sz_repo_cli/pubspec.lock
@@ -57,6 +57,14 @@ packages:
       url: "https://pub.dev"
     source: hosted
     version: "0.4.0"
+  clock:
+    dependency: "direct main"
+    description:
+      name: clock
+      sha256: cb6d7f03e1de671e34607e909a7213e31d7752be4fb66a86d29fe1eb14bfb5cf
+      url: "https://pub.dev"
+    source: hosted
+    version: "1.1.1"
   collection:
     dependency: transitive
     description:
diff --git a/tools/sz_repo_cli/pubspec.yaml b/tools/sz_repo_cli/pubspec.yaml
index 40cadc575..576be3455 100644
--- a/tools/sz_repo_cli/pubspec.yaml
+++ b/tools/sz_repo_cli/pubspec.yaml
@@ -34,6 +34,7 @@ dependencies:
   process: ^5.0.1
   process_runner: ^4.1.4
   file: ^7.0.0
+  clock: ^1.1.1
 
 dev_dependencies:
   sharezone_lints: