You can already let the player stop after finishing the running song. I think it would be useful to have a function to let it stop playing after a certain amount of time or tracks. This could be integrated in the menu when you rightclick on the running track. There could be a submenu for "Stop after X" with the options "Time" (enter minutes or time of day), "Running song" (which is already integrated) and "Number of tracks". Alternatively you could rightclick in the playlist and set a stop marker on a specific song.