In my opinion, there's a mistake in that phrase. I see two possibilities here:
That the phrase should read:
"Accept submissions deadline should be set after the OPENING date".
If this is the case, this would mean that any deadline for submissions of reports, projects, etc. should be set after the course has started. Opening date = start date.
I think this is the problem, because normally, if you say "open date", it usually means a day (a date) that is free to schedule an event or a class. Open date = a day where no event is scheduled yet.
Hope this helps! By the way, I'm learning Russian! Ha ha, would love if you added me as a friend, we can help each other out or talk live for even quicker progress!