Question: how long does it take to cook a prime rib at 325 degrees?
Answer: The bones create a natural roasting rack for the meat, so don't worry if you don't have one. Cook the roast for 15 minutes, then reduce the oven temperature to 325 degrees. Continue to cook the roast until your meat thermometer reads 120 degrees. Estimate about 15 minutes of cooking time per pound of prime rib.