The general cooking time for my oven is 3 hours per 3 pounds of brisket, adding an additional hour per pound beyond that. Since ovens vary, the temperature will be your way of gauging when your brisket is done. For best results, insert an ovenproof meat thermometer prior to roasting into the thickest part of the brisket. Leave the thermometer in throughout the cooking process. You can also insert an instant-read thermometer toward end of cooking time for about 15 seconds to get an accurate reading.