I already finish my 7 day dev period, from the 5th to the 11th, but there is a game crashing bug I overlooked. can I post a fix before the grading period is over, or do I have to wait? 

We request you maintain a 7DRL version of your game for reference.  People judging may elect to play either that one or  the latest.  Change notes can specify what was fixed / added so the judges can take that into account even if they play the latest version.

You can direct people to the latest & best version, however, as we'd want the normal players of your game to have the best experience as possible.

Follow-up question to this, I submitted my game about an hour before my 7 day period was up, then quickly uploaded a bug fix right after, still within my 7 day window. Is it possible to indicate for the judges to use this version, or is it locked to the one that was in at the time of submission?

The 7drl one can be whatever is in your 168 hour window.  So if you get a second build within the 168 hour window, feel free to replace the previous upload.

Stupid itch.io. I changed the display name of my zip file so I could upload a fixed version. itch.io replaced the file. So I grabbed my git repo from Friday night and rebuilt it and uploaded the 7drl version.

It's against the spirit of the challenge. Far too easy to "just put that off till after release".    

I have uploaded a fixed version, but both the 7DRL build and the patched version are available for download and play. I have clearly notated which is which