There is a good documentaion at cppreference.com

General

• Use duration::count() only for legacy code and debugging
• Use explicit casts (duration_cast and timepoint_cast) only when precission loss is required
  • lossless conversions are implicit
  • duration_cast truncates towards zero

Clocks

• system_clock:
  • wall Clock
  • calendar
• steady_clock:
  • stop watch
  • for timing measurements
• high_resolution_clock:
  • usually a type alias to one of the other two types

Date

• Main type year/month/day:
• errors are either
  • caught at compile time or
  • can be detected at runtime with .ok() (needs to be done by user!)