In some places in iroha_data_model, structures use Duration for data which doesn't mean a span of time, but actually means a timestamp. Examples:

• start:

  iroha/data_model/src/events/time.rs

  Lines 100 to 105 in 4362c94

  	pub struct Schedule {
  	/// The first execution time
  	pub start: Duration,
  	/// If some, the period between cyclic executions
  	pub period: Option<Duration>,
  	}

• since:

  iroha/data_model/src/events/time.rs

  Lines 126 to 131 in 4362c94

  	pub struct TimeInterval {
  	/// The start of a time interval
  	pub since: Duration,
  	/// The length of a time interval
  	pub length: Duration,
  	}

These fields are timestamps, not time spans.

I propose to use a structure that is designed specifically for timestamps, e.g. chrono::DateTime.