Hello there, my crew and I are working on a graphic novel to post here for the jam. But we are still on the "polishing phase" 

My main question was: are we allowed to submit our game even if we are overdue? 

When the jam ends on April 30th (around 30 hours at the time of me posting this reply), you won't be able to submit it. You have to submit it before the jam's end.

But! You also have the option of submitting it before the end date even if its unfinished, because you can still edit it even after the jam ends, but only if you were able to submit it before it ends!