I end up needing to check a bag for about 75% of my domestic trips. Overwhelmingly, my experience in the last couple years has been that my bag arrives well before the 20 minutes is up, and usually in the first 20 or so bags on the belt. There are specific airports where I know yellow tagged bags typically don't come first, typically smaller airports where the bags are not handled by Delta ground staff. Never had any signs of damage, but it would be really hard to damage my bag anyway. I've had one lost bag, which was the result of IRROPs and accepting a rerouting via Twitter then changing to a better reroute once I got through on the PM line. The bag got retagged for the first reroute I accepted, which arrived 2 hours later.
FWIW, just a few weeks ago I was watching a bunch of bags get loaded on my SLC-DTW flight. I could see the ground crew checking all of the tags and grabbing the non-SP bags first and loading them into the forward hold. It seemed all the SP tagged bags went in the rear hold. So in this case, they were at least keeping them separate. Of course, that doesn't mean the DTW crews did anything with the nicely organized luggage.