About

A duration is the period of time between two event occurrences, computed as the difference of the time coordinates of those events.

A duration is an amount of time that may be expressed in terms of unit of time

• in a day-based fashion (ie 2 days 3 hour ..)
• or in a time-based fashion, such as 45.7 seconds.

Elapsed time (wall clock) is a duration needed to perform a task.

Negative

A duration may be negative because of the leap second ¹⁾