Your boneless prime rib cooking time will depend on the size of roast you're making: 4 lb. roast: 15 minute sear + 1 hour 40 minutes cook time 5 lb. roast: 15 minute sear + 1 hour 45 minutes cook time 6 lb. roast: 15 minute sear + 1 hour 50 minutes cook time
The ideal cooking temperatures for a prime rib roast are 325°F and 10-15 minutes per pound. However, you may even prepare prime rib roasts at temperatures as low as 200°F, but keep in mind that the meat will take a long time to cook through fully.
“The Slow Roast Method for roasting prime rib is easy, hands-off, and foolproof. Roasting at a low temp ensures that the meat cooks evenly throughout, rather than with a well done exterior and a rare interior. This method also leaves you time to get everything else ready while the meat slowly cooks to perfection.” — Joan Velush
If for the sake of time you have to cook it the day before, then undercook it so that when you heat it up it will hopefully come out at the doneness you prefer. The best way to store your leftover Prime Rib is to wrap it well before putting it into the refrigerator.