Wow, totally forgot about this until it was too late, shame too it's a really cool idea.

One suggestion, you could make the actual window of the jam longer than 30 minutes, then  people could pick and choose how they allocate their 30 minutes (and lessen the chance of people missing it altogether). 

This means you'd have to rely on an honour system for people actually sticking to the time frame, but there's a 3 Hour game jam on itch (Trijam) that seems to handle it pretty well.

Will definitely try to remember this is happening if you run this again :P (hope you do!).

-Jimmy