Be more vague about build time

Build time depends on many factors and evolves as Slicer does

{{cookiecutter.project_name}}/BUILD_WINDOWS.md

@@ -35,7 +35,7 @@ Note: use short source and build directory names to avoid the [maximum path leng
 
 Build
 -----
-Note: The build process will take approximately 3 hours.
+Note: The build process can take hours.
 
 <b>Option 1: CMake GUI and Visual Studio (Recommended)</b>