Cook until the ham reaches an internal temperature of 160 degrees F. Remove from oven, cover loosely with aluminum foil, and let sit approximately 15 to 20 minutes. NOTE: Cutting into the meat too early will cause a significant loss of juice.rain, glaze, and brown at 400 F 15 minutes.) 10 to 16, whole; 5 to 8, half 20 to 25 PRE-COOKED HAM A precooked ham does not have to be cooked, but will taste better if you heat it thoroughly to an internal temperature of 140 degrees F. (60 C).