Question: how long does it take to cook a prime rib at 250 degrees?
Answer: In a 150°F oven, this will take around 5 1/2 to 6 1/2 hours; in a 250°F oven, this will take 3 1/2 to 4 hours. Remove roast from oven and tent loosely with aluminum foil. Place in a warm spot in the kitchen and allow to rest for at least 30 minutes and up to 1 1/2 hours.