Help cooking for 150 people

Hello I have been asked to cook Boneless Prime Rib for 150 people this weekend and as I have prepared small prime rib roasts before and some as large as 16 lbs., to have to cook it for 150 people is totally different. I have 150 pounds of boneless prime rib that I am picking up on Thursday to season. I am wondering what time I would have to put the 150 pounds of prime rib in the oven to be ready to serve at 6:30 P.M.? Please any help would be greatly appreciated!!!
Thank you.