I don't know what Densanon779 has to say about this, but, honestly, I don't think there's anything wrong with getting a head start on this jam, especially if you're motivated to do so, and I don't think there's anything wrong with using the time that the rest of us have to complete whatever you're working on. I don't think anyone here will give you a hard time, especially since there's no rule saying that you can't start early. Hell, I probably would have if I managed to think of a good idea before now. xD;
If you aren't finished with your project yet though, I would hold off on submitting it until you're done. If you want some feedback though, I'm sure that there are plenty of people here who wouldn't mind playtesting whatever you're making right now and giving you some critique (myself included), so it might be better to ask for that instead instead of putting up a half-baked work.