The MMAPI javadocs explains it as well as it can be:
http://www.j2medev.com/api/mmapi/javax/microedition/media/Player.html or simply browse the WTK docs directory.
setMediaTime() is used for example in audio/video playback
to set the starting playing time, before a player is realized.
StopTimeControl is also related to media time,
it allows you to set the media's stop time.
http://www.j2medev.com/api/mmapi/javax/microedition/media/control/StopTimeControl.html [ June 25, 2006: Message edited by: Eduardo Marques ]