Just to give you a flavor of the commands nice and at, here's an example that would run the trace program in the background and at a reduced priority at three in the morning: 

	sexyrobot% at 3
	nice /homes/isgi/ben/trace/trace -oMyPicture.rgb MyScene.iv
	^D

That will give you a warning message that the commands will be run by the Bourne shell (sh); however, that's fine. Any output would be emailed to you. You should read the actual man pages for at and nice for the full details.