C++ library written by Howard Hinnant, merged into the C++ standard over four committee cycles. Separates three concerns: (1) duration — a representation plus a compile-time std::ratio to seconds (milliseconds, nanoseconds, 60 fps, NTSC frames are all just new ratio types); (2) time_point — a duration paired with a clock (system_clock, steady_clock, atomic clock, or user-defined) so a value always has a starting point; (3) calendars — entirely separate abstractions (Gregorian, Julian, ISO week, Chinese) with convenience structs for weekday/year-week/etc. Refuses auto-conversions like '31 Jan + 1 month' because the correct answer depends on domain (tax software vs Google Calendar vs scheduling). Arithmetic rules encode semantics: time_point − time_point = duration, time_point + duration = time_point, time_point + time_point = compile error. Daylight savings time is layered on top as a separate concern. All type checking happens at compile time, so generated code matches hand-rolled performant C. Wójtowicz recommends porting the ideas — not the syntax — to other languages, including Ruby.