3. Place the burgers on the grill, close the lid, and cook for 4 to 6 minutes. Turn the burgers and cook for an additional 4 minutes for a medium-pink doneness. If you want a well-done burger, cook for 12 to 15 minutes. They should start to feel firm when pressed. If you want to use an instant-read thermometer, do like the health inspectors do and go in through the side, not the top.