if playing the level takes 20 seconds (or there's a fail condition after 20 seconds)

Though i would encourage you to just try and build a game for the jam, maybe reusing existing mechanics.

Sl1ngshot’s answer is good!

We don’t want to see games you’ve released previously submitted here with only tiny alterations. You are however quite welcome to use your proven mechanics and the coding for them.

But at the very least, please make a new level. This jam is a good opportunity to experiment so consider trying some new and wacky idea with your mechanic that might not have been a fit for your original game