Tim mentioned in the original stream that even for bug fixes after the deadline, it's all "based on the honour system." Possibly others have a different opinion on the following, but mine is that I don't feel it's against the spirit of the jam to submit a working prototype a few days early, followed by updated versions closer to the deadline, as long as you aren't polishing after the deadline. I compare it to Olympic powerlifters, who generally do an easier first lift just to get something on the board in case their second lift fails.
In short, as long as what you're submitting now is a playable build, I don't see anybody coming after you with torches and pitchforks =)