It takes from 25 to 30 minutes to fully cook chicken breasts on the grill.
Place the chicken breast on the grill and close the lid for 15 minutes to let one side of the chicken breast cook and then after minutes open the lid to the grill and flip the chicken breast over and let it cook again for another 10 to 15 minutes.
The chicken breast meat should no longer be pink or even better use a meat thermometer to check for an internal temperature of 170 F minimum.
Any less temperature than that then the chicken needs to cook longer.
But usually 30 minutes is long enough to fully cook chicken on the grill.