My iPhone changes time zones automatically twice a week, when I cross from Mountain to Pacific, and back. It even knows that the timezone change is not the Alberta/BC border. It's very accurate, and I'm assuming it uses info from cell towers for the time change. (Actually, I know it does, because my ipad doesn't change until I pick up a wifi signal) That's where I would start my hunt. See where you are when the time changes, and see if you can nail it down to a particular place.