Note: Cooking times can be tricky as each crock pot is different. If cooking from a thawed state, I find that around 5 hours is perfect with my crock pot. However, if breasts are frozen, it takes 7 or 8 hours. My old crock pot took 7 hours to cook from thawed.
It is also tricky to tell if the chicken is cooked because of the red elements in the stew. I usually choose the largest piece I can find, pull it out and cut it. You can tell if it is done by the texture of the chicken. It should have layers like a croissant. if the center is smooth and shiny, the chicken is not cooked through.