Help! put in 16 lb turkey at 11am and now at 1 pm (3 hrs) its thermometer popped up. is it done?

the package said between 5-6 hrs and the thermometer comes up at 3? is that because it was at room temp from thawing? is it done so early? I know those little plastic thermometer pop up things don't work well sometimes but how can I be sure the food is done and safe for my family?