A standard three-pound top round roast needs around 30 minutes in a 375° F oven to become rare. But it's not time that matters when cooking meat, it's temperature. And every oven and cut of meat will cook slightly differently. If you prefer your roast rare, cook it until a thermometer reads 125° F. For medium or medium-well, cooking times can take up to 45 minutes or even more. Until you get to know your oven with a specific cut, check the internal temperature of the roast with a probe thermometer inserted into the thickest part.