The time it takes to cook a 24 lb Turkey is between 4-1/2 to 5 hours.
When cooking or baking a Turkey you cook the turkey for 20 minutes for each lb of Turkey you are cooking.
If you're baking a turkey you should bake the Turkey at a minimum of 350 F degrees.
For example a 5 lb Turkey would take 100 minutes to cook.
A 10 lb Turkey should take at least 200 minutes to cook and so on and so forth.
As long as you're cooking the Turkey for at least 20 minutes per lb of weight of the turkey it should be fully cooked.
When a turkey is fully cooked the turkeys internal temperature should reach 180°F
If you do not have a meat thermometer you can check the turkey for doneness without a thermometer, pierce the thigh and pay attention to the juices: if the juices run clear the turkey is cooked and if the juices are reddish pink the turkey needs cooked longer.