Are we allowed to build our game for more plattforms after deadline? A windows 10 build is much faster than html5, so if I build it for windows, to get it out, can we then build the game for additional platforms after the deadline?

Unfortunately no. There's no way to just allow builds for different platforms, so I would have to allow entrants to upload any new files, which means they could keep working on and updating their game through the rating period. Uploads will lock at the end of the jam and unlock after the rating period is over.