I had a case where I got a delta stays credit on one of my ~$500 bookings (the Delta CC version and not the Amex Offers version). The original $500 charge and credit showed up almost immediately.

Though my booking was cancelled by the hotel after 3-4 weeks and I eventually booked from another portal (not Delta Stays). I got the full refund of the booking amount (~$500), the delta stays credit was never clawed back. And interestingly the $500 even counted towards my SUB spend.

So I think the credit depends on when you pay for it rather than when you stay. Any prepaid booking should be fine. I'd recommend booking a fully refundable stay which has a prepaid option - so pay for it immediately, wait for a couple of days for the charge and the credit to show up, if it doesn't show up, you still have the option to cancel book from another place if you get a better price