Heard from itch.io email as well. I have decided to take part, really nervous about not having the time... 9hrs to think of an idea.
Don't stress! We're a very relaxed jam. If you like, you can spend a few days thinking, and just ask for a late submission link. :) Our times and dates are just for people to get together and share their process, but lots of people start early or finish late! Last year I did my entry on weekends only and submitted in December :)