AbsoluteTime

AbsoluteTime[ ] gives the total number of seconds since the beginning of January 1, 1900, in your time zone.

AbsoluteTime[ ] uses whatever date and time have been set on your computer system. It performs no corrections for time zones, daylight saving time, etc.

AbsoluteTime[z] gives the date in time zone z. This is inferred by knowing your local date and time, and local time zone. The time zone is given as the number of hours to be added to Greenwich mean time to obtain local time.

AbsoluteTime[ ] is accurate only down to a granularity of at least $TimeUnit seconds.

There are 2208988800 seconds from the beginning of January 1, 1900 to the beginning of January 1, 1970 and 2840140800 seconds to the beginning of January 1, 1990.

See The Mathematica Book: Section 2.13.3.

See also: Date, SessionTime, TimeUsed, Timing, TimeZone, ToDate, FromDate.

Related package: Miscellaneous`Calendar`.