I took a part in demoscene-related activity for some time.. It wasn't unusual for audio/music guys there to compete with each other in short contests where you need to compose a music track in a limited time, using a proposed theme or a sample pack. The time limit usually varied from an hour to a day.
This was pretty fun.
I'd definitely be down for something like this. I mean I know we have the biweekly themed composition contest, but having an hour-long compo each week would be fun, and I'm sure it would help people to stretch and grow.