A note on Timers: Standard Timer - specify an interval to run the library update process.
It will be launched every X hours within the interval unless on of the conditions specified by you as been met (don't run during media playback, etc) in which case it will be run at the next earliest convenience.
Advanced Timer - specify a cron expression to use as an interval for the update process.
This is an XBMC Service that will update your music and video libraries on a timer.
You can select a different interval to scan your media databases (Audio, Video, Both) or you can set a cron-style timer for greater control.