it says on the main page that once you submit your game you will not be allowed to edit it unless there are severe bugs, So make sure you are satisfied with your game before submitting. Other than that submit anytime before the final deadline.
Viewing post in When are we supposed to "Submit"?
Hi! Apologies for missing this discussion, but you can edit your build anytime until the deadline passes. That is, feel free to upload and update your game as many times as you need until the submission period ends (which unfortunately is in 2.5 hours... really wish the email about this topic would’ve come through!)