You may start hacking anytime January 5th local time. You must stop work on your connected app and add it to the Projects tab of this site by midnight, January 6th. If you're crazy and don't sleep at all, this means you have exactly 48 hours to work on your hack. But for your own sake, please get some sleep.
Official site schedule (SF/NYC)
On January 5th (in local time)
09:00 - Office opens / Snacks / Get oriented
10:00 - Partner API presentations / Rules review / 30 sec idea pitches
13:00 - Lunch
20:00 in SF - (8 pm) Beers+Demos / Voting / Site prizes announced / Decompression (We're starting SF early to accommodate people from the South Bay)
21:00 in NYC - (9 pm) Beers+Demos / Voting / Site prizes announced / Decompression
23:00 - Go home!
On January 6th
??:?? - The office won't be open, but feel free to put a little spit and polish into your connected app and submit it for a global prize!