Export and test a few hours before the submission. I know there's a few hours left and you could use those to develop the game further, but there's a plethora of things that can go wrong in an export that doesn't happen in an engine build, and the sooner you figure out which bugs are only in the export the better. We had a pretty bad one we found where the game closed when trying to go to the next level or retrying from game over, but we found exporting as a DEBUG solved it. I don't know if this is something we messed up or a quirk of Godot 4.
Additionally Git was a lifesaver, I haven't had the chance to properly use it in a project before because I was a little scared to use it, but it sped up the process a lot! As long as you stick to your branches, discard unnecessary changes, and back up before merging to main, you should be fine. I used the GitHub desktop app and I don't much like it, but it was free. And if you're using Godot, please close the project before pulling!