Chicken Thighs cook fully in as little as 15 minutes on the grill while Chicken Legs can take as long as 45 minutes to be fully cooked on the grill.
You can be sure that the chicken is fully cooked by using a food probe thermometer and checking the internal temperature of the chicken and if the chickens internal temperature is 180 F or higher when the thermometer is inserted into the thickest part of the meat then the chicken is done and ready to eat.