Calendars, Dates, Time Modules add-subtract-date - add units of time (ex. 3 days) to dates convert-hrtime - pretty high-resolution time as seconds, milliseconds, nanoseconds date-time - pretty datetime leap-year - check if a year is a leap year month-days - get the number of days in a particular month parse-ms - convert milliseconds into time parts (days, hours, seconds, etc.) pretty-ms - human readable version of milliseconds sec - convert a datetime string to seconds time-zone - human readable timezone to-milliseconds - convert time parts to milliseconds weeknumber - get week number or day number of the year year-days - get number of days in a particular year (365 vs. 366)