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40.10 Time Calculations

These functions perform calendrical computations using time values (see Time of Day). A value of nil for any of their time-value arguments stands for the current system time, and a single integer number stands for the number of seconds since the epoch.

— Function: time-less-p t1 t2

This returns t if time value t1 is less than time value t2.

— Function: time-subtract t1 t2

This returns the time difference t1 − t2 between two time values, as a time value. If you need the difference in units of elapsed seconds, use float-time (see float-time) to convert the result into seconds.

— Function: time-add t1 t2

This returns the sum of two time values, as a time value. One argument should represent a time difference rather than a point in time, either as a list or as a single number of elapsed seconds. Here is how to add a number of seconds to a time value: 

          (time-add time seconds)
— Function: time-to-days time-value

This function returns the number of days between the beginning of year 1 and time-value.

— Function: time-to-day-in-year time-value

This returns the day number within the year corresponding to time-value.

— Function: date-leap-year-p year

This function returns t if year is a leap year.