Sure I know the mockups are the main point of the jam but is it ok if I get ahead of myself and also put the prototype/playable something on the page as well even if it doesn't matter? I might have the free time anyway. I'm saying this cuz I usually mockup directly into unity with half-playable stuff and buttons clicking but not doing much, etc, and sometime there is some gameplay too.

You can definitly work on the game, but I'd ask to wait at least a couple of days after the end of the jam, just to keep in the spirit of it.