If the chicken breasts in your market are larger than 1/4 lb. each, they will take longer to cook. Be sure to cook them long enough so that they are no longer pink in the centers and the juices run clear (165°F).
How to Safely Handle Raw Chicken
Always wash hands, preparation surfaces and utensils in hot, soapy water before and after contact with raw chicken. Dry hands and surfaces with a clean towel or paper towels. Take special care in washing worn cutting boards as there may be hard-to-clean grooves or cracks that can collect bacteria.