If you want Tracks to play for a set period of time and gradually fade and optionally shut down your computer, you can use the Sleep function:

Note: If shutting down the computer, it's a good idea to close all other applications beforehand, since some applications may ask for a confirmation that would prevent the computer from shutting down.

Page url: http://www.mediamonkey.com/sw/webhelp/frame/index.html?sleep.htm