Ideally, you want the tip of the thermometer to be in the center of the roast. Remove the roast when the meat's internal temperature reaches 160 degrees F. A four-pound roast may take one-and-three-quarters of an hour to two hours to cook.Let the roast set for about 15 minutes after removing it from the oven and before carving. If the pork roast is done, the meat will be whitish, not pink. four-pound roast may take one-and-three-quarters of an hour to two hours to cook. Let the roast set for about 15 minutes after removing it from the oven and before carving. If the pork roast is done, the meat will be whitish, not pink.