When roasting a turkey it takes around 20 minutes per each lb of the turkey to be fully cooked and well done.
For example if you have a 15 lb Turkey that you need to bake or roast then it can take you 300 minutes of cooking time to roast or bake the 15 lb Turkey to well done.
Also if you have a stuffed Turkey it takes an additional 30 minutes to cook the stuffed turkey versus the non stuffed turkey.
Some Turkeys come with a pop up thing that pops up when the Turkey is fully cooked and well done.
When roasting a Turkey to well done or baking a Turkey to well done figure on about 4 to 6 hours to fully cook the turkey to well done.
Turkeys take a pretty long time to cook and if it's frozen it will take longer to cook the turkey than it would take if the Turkey was thawed out first.
I like to thaw the turkey out 24 hours the day before in the refrigerator so that it's ready to cook and cooks more evenly and faster.
I bake my turkeys at a 400 F temperature for 5 hours which is usually enough time for the Turkey to be well done.
Also check the Turkey cavity for a giblet package that can be in paper or plastic that could melt and burn in the Turkey.