Every Saturday at 20:00 UTC. The time in your local time and a countdown-timer should be in the top of the site though.
No. Keep working on your game until it's done, then submit.
You are free to use premade assets but it is recommended that you make at least one game from scratch. Some assets are provided on the assets page.
Yes, you'll need to host the game and submit the links here. We do host the thumbnail though. If you don't have a website yourself, use something like dropbox / google drive, or itch.io / newgrounds. Ask in IRC for more suggestions.
About 30 minutes after the jam ends, we host a stream on Twitch where all submitted games are played. The stream usually lasts about 2 hours. It's not always the same people streaming though, so keep an eye on the IRC channel to see who's streaming.
If you finish and submit your game before the stream ends, we'll play it on stream, even if it took you more than an hour to finish.
If you come late you can still participate. If the stream is over, then your game won't be played on-stream, obviously, but we'll still keep it on the site!
You retain full ownership / copyright / yadda yadda. If you get a BAFTA make sure to mention us in your acceptance speech though :D