Normally I find that chicken quarters are going to take at least an hour more like 1 1/2 hours. But this is depending on how much coals you get going in the basket. It is important to have a strong bed of coals when cooking chicken in the PBC. Especially when there is a lot of chicken. There will be a lot of dripping onto those coals and that will cool the heat some.
If you can leave one rebar out. This will increase the temp about 50F in my experience.
You can also crack the lid slightly the last 10 minutes to help finish the skin. I like to remove the lid the last 5 minutes to do this but you must keep your eyes on it because you could end up with charred chicken very quickly!
Because of the way the PBC cooks it is tough to overcook the chicken. The grease fog helps keep the chicken from drying out creating a rich, humid, and flavorful environment to cook it. I would start checking the quarters after the first hour and every 10 minutes after that.
Good luck and don't forget to post pics of your cook