The cooking time for prime rib depends on the weight of the roast and the desired level of doneness. Here is a general guideline based on oven temperature and internal temperature targets:

• Start by roasting the prime rib at a high temperature (around 500°F) for 15 to 25 minutes to develop a crust.
• Then reduce the oven temperature to about 300-325°F and continue cooking.
• The approximate cooking time at the lower temperature is about 10-15 minutes per pound, depending on how rare or well-done you want it:
  • Rare: 10-12 minutes per pound, internal temperature 115-120°F
  • Medium rare: 13-14 minutes per pound, internal temperature 125-130°F
  • Medium: 14-15 minutes per pound, internal temperature 135-140°F
  • Medium well: about 15 minutes per pound, internal temperature 145-150°F

Use a meat thermometer inserted into the thickest part of the roast (not touching bone) to check the internal temperature. Remove the roast from the oven 5-10°F before it reaches your target temperature, as it will continue to cook while resting. Rest the prime rib for about 20-30 minutes covered loosely with foil before carving to allow juices to redistribute. For example, a 5-pound prime rib cooked medium rare would take roughly 15 minutes at 500°F, then about 65-70 minutes at 325°F, followed by resting

. Some methods suggest starting at a lower temperature (around 225°F) for slow roasting, then finishing with a high-heat roast or sear to develop the crust, which can take about 35 minutes per pound at the low temp plus a final high- heat roast of several minutes

. In summary, total cooking time varies but generally ranges from 1.5 to 3 hours depending on size and desired doneness, with key steps being an initial high-heat roast, a lower temperature cooking phase, and resting before carving. A meat thermometer is essential for perfect results.