I had a chance to secure a few tips from the folks who sponsor the contest. They are below. If you attempt this challenge, good luck!
Everyone approaches 3-Day differently ---
some have a detailed outline,
some have none at all,
some write 20 hours a day,
some keep a healthy schedule.
But here's some general advice:
1. Go in with a very light outline, or 'storyboard'. Consider writing notes on each chapter on recipe cards and taping them to the wall above your computer. Then be prepared to abandon your outline or to sacrifice plot points if inspiration takes you or you are running out of time.
2. Get a decent amount of sleep, make sure to stock the fridge with some quick, healthy snacks, and get outside for a walk at least once a day--that will help refill the creative well.
3. Keep your expectations reasonable! This is a creative experiment. Don't expect to produce the Great North American Novel.
4. Leave time for a quick read-over and proof on Monday night, but don't read too deep or get too hung up on editing. You'll just freak yourself out, and the judges expect it to be rough.