PLEASE READ this regarding TEMP & TIME! There is no "right" temperature. If you roast it at 250°F it will just take longer to cook than at 325°F. (Just like picking High or Low on a crock-pot) I cannot tell you exactly how long it will take. It depends on what type of oven you have & how warm/cold your turkey is when you put it in the oven. You HAVE to use an instant read thermometer to know when it is cooked. (I roast my 18-20 lbs. fresh turkey at 250°F. It took about 4 hours to reach the correct temperature in my old convection oven. It took 5 hours in my new one.) Because of the mayo, the skin is crisp and flavorful and the meat is tender, moist and delicious. If you don't use the butter & broth, you will not have enough pan drippings to make gravy. I've also added 1/2 cup of beer or wine to the mixture before & it was also spectacular. With slow roasting it, the meat stays so juicy I've actually had it squirt out when I insert the thermometer! I've never had a better turkey.