Aside from the launch day, Apple stores should be opening at their regular store ours, though people are still showing up pretty early looking for the new iPHones. I recommend purchasing for an in store pickup online once their stock is "available in stores today". That way it will be reserved for you and you can get it at any time without hassle.
Make sure you check their availability at night after they close or in the morning before they open when they get their new shipment in.