Can I submit it early? I don't think I can come up with an idea and not develop it until december 9th.
hmm well submissions won't be open until the date (that's just how this website (itch.io) works with jams). You can definitely make the game page and all that on itch side (which is what you submit) and then post about it in the forum here + the discord. then when the submissions open throw it in the list!