how long cook prime rib per pound
1 APPROXIMATE COOKING TIMES for the prime rib cooked at 350Â°F after the 20 minute cooking time at 450Â°F. 2  Rare; cook 12-13 minutes per pound or to 130Â°F.  Medium-rare; cook 14-16 minutes per pound or to 140Â°F (I would not recommend cooking a prime rib any more than medium-rare).