Cooking chicken on a gas grill takes between 10 to 20 minutes depending on how well done you want the chicken to be.
For me I like to cook my chicken on the gas grill for 30 minutes though instead of 20 minutes because it's the way I like my chicken.
So I place the chicken on the grill grate and then leave a 1/2 inch space between the chicken.
I then turn the chicken over every 5 minutes until the 30 minutes is up and then the chicken is well done for me.
Some people are okay with their chicken done at 15 to 20 minutes of cooking time which is usually good enough for them.
However I just like my grilled chicken a little more done.
But 15 to 20 minutes on the grill will fully cook the chicken to where it's safe to eat.