The presentation describes the complexities involved in timekeeping. It touches on, among other things, the various time units, time zones, daylight saving time, leap seconds and other surprises lurking for programmers, as well as related errors. The audience will gain a better understanding of the rules governing calendars, time differences and the impact of daylight saving time on software. Attendees should gain knowledge of practical applications, such as correctly formatting dates and times in different contexts and using the right API for the right purpose.