2.1.1245 Part 1 Section 20.1.3.3, end (Audio End Time)

a.   The standard uses common attribute descriptions for 'time' and 'track' that are shared by both 'st' and 'end' elements.

In Office, the time attribute specifies the time in seconds that the CD audio should be started on at or stopped at while the track attribute specifies the track of the CD the audio will begin on or stop at.