I was out of town and we go to a resteraunt that says they slow cook their prime rib overnight. They run a special on Saturday night only for this. Let me tell you it is the best and most tender prime rib I have had in about 30 years when a resteraunt where I live used to do it. The sizes are 12 oz, 18 oz, and 24 oz. I usually get the 18 oz and they are about 1 1/2 inches thick and perfect medium all the way through. It melts in your mouth. I asked them if they sell their rub or if they would tell me what was in it and they said they do not sell it and it is a secret. When I do a prime rib in the smoker at 225 it takes 3-4 hours when I pull it at 135. Does anyone know how this can be cooked overnight and sit most of the next day until supper time and still have it the way you want it? I would think even if they cooked it at 150 it would take maybe 6-7 hours.