If you are cooking a larger than average turkey (18 to 25 pounds) for your midday Christmas dinner, you may put it in your oven before you go to bed Christmas Eve. Prepare the turkey as usual and place it in your roasting pan. Cover it loosely with aluminum foil, turn the oven to 250 degrees and forget it until a couple hours before mealtime. You will want to remove the foil and baste with the drippings until gravy making time.