A rack of pork ribs that weighs 3 pounds takes around 3 hours to cook. This includes approximately 1 hour per pound plus an added 15 to 30 minutes to tenderize the meat. Continue Reading. To cook ribs in the oven, first defrost them for approximately 30 minutes. After preheating the oven to 225 degrees Fahrenheit, prepare the ribs by first removing the white membrane on the back of the ribs.