Beef short ribs whole or beef back ribs? By the weight I'm assuming short ribs. Last time I did them (choice 3-bone rack whole cryovac, 7.5 lbs) they took about 12 hours at 225 to get to 190-195 and were tender and delicious. The variation in meat thickness across the rack merits checking as they start to get done so the thinner end pieces don't overcook. As Jobiewan says, done early and FTC'd is better than done late. I'm not sure if "two pieces" means two ribs and one rib or what. I've only seen three-rib racks. But the pieces are large, so maybe an hour or two earlier to start checking temp. Good luck!