I know at SUNY upstate, they have a interview cancelation list. My interview is scheduled for Mar 21, but when someone cancels an interview, they go to the list of names, such as me, and then ask teh first person who has agreed to only need X days of notification to come down. As for me, I said that I would need two days, as I live in Canada about 4 hours away.
Other schools probably do this type of thing too.