There's a voting period so no updates during the voting period, and you can make minor updates before the stream (like bugfixes).
But after that you can pretty much do whatever you want. But the deadline is today, if you haven't finished feel free to submit what you have - cause submissions will be locked after that.
Yeah I'm not sure why you are unable to accept the invite - you would want to contact discord support to get it sorted out - It could be a number of reasons.