Version: (using KDE KDE 3.3.0) Installed from: Compiled From Sources A kind of Auto DJ function like they use it in Music Match Jukebox would be fine. You enter a time you want to listen to music (like 3 hours) and preferences (like artists, albums or rating) and the program fetches the tracks to fullfill your wish automatically. You don't have to fill the playlist by hand. Perhaps just take a look at the music match software (if you know somebody who still has windows installed)
Aside from the length criteria, this has already been done using smart playlists. Additionally, i am marking this as a duplicate since bug 92630 is more specific to time restrictions on smart playlists. *** This bug has been marked as a duplicate of 92630 ***