I've mostly settled on a first round posting period of Jan 1-Feb 7 (post whenever you want within that window). You don't have to be done by Jan 1, you're just allowed to post then if you are done with a fic. Since the limited prompt list will grow as new fic get submitted, hopefully people will continue being inspired and keep writing :) If the bilingual ficathon can match or exceed what the last two monolingual ficathons put out, we might have fifty fics or more, and I don't see a real need to bunch them. Drabbles will be accepted as well as longer fics.
I was initially considering Dec 21-31 for initial prompt submission (one prompt per person, starting out, so fics get written for the broadest possible range of people). But given that's a period of time when everyone is highly distracted by Other Fandom Events, Dec 1-14 might be preferable? I am particularly interested in your input if you're doing Yuletide.
Edit: or we could have it all month and be really laid back. That might work too.