Place the roast in a roasting pan with the fatty side up. In a small bowl, mix together the garlic, olive oil, salt, pepper and thyme. Spread the mixture over the fatty layer of the roast, and let the roast sit out until it is at room temperature, no longer than 1 hour.

Preheat the oven to 460 degrees F.

Bake the roast for 12 minutes in the preheated oven, then reduce the temperature to 400 for 8 minutes and finally reduce the temperature to 325 degrees F, and continue roasting for 20 minutes for each pound of prime rib. The internal temperature of the roast should be at 130 degrees F for medium rare. 

Allow the roast to rest for 15 minutes before carving so the meat can retain its juices and to finish cooking to a medium rare temperature.

 For a smaller prime rib you can still use a lot of the marinade to get good coverage and flavor.

For a smaller prime rib cook the roast a little longer, to an internal temp of 133, to have a medium rare rib after it sits.