I always buy Butterball turkey's because they come with directions and they are no fail (I've done over 20 of their turkeys).
At 325 unstuffed and uncovered you are looking at 4 hours plus or minus half an hour. Doneness is determined by temperature. You want the breast at 165 and the thigh at 180. Getting the thermometer in the thigh at the right place is a little tricky.
"The tip of the meat thermometer should be placed in the thigh muscle just above and beyond the lower part of the thighbone but not touching the bone, and it should be pointing toward the body. For the stuffing temperature, the tip of the thermometer should be in the center of the body cavity." http://www.butterball.com/tips-how-t...turkey-is-done
Cover the breast with foil about 2/3 the way through cooking.