That is back to back ticketing. And yes, Delta prohibits it. You will no doubt find people on this board who will tell you do it anyway/Delta doesn't care that much/don't enter your SkyMiles number and you'll be fine/etc.
This is insane. So I book my scheduled Thurs-Monday travel to JAX to visit family which is booked well in advance because that schedule is set. Then maybe a week before we decide to make a trip to Chicago to visit friends for Friday-Sunday. This isn't allowed?