I'm going to brag here. We have one post office that is next to the airport. it opens at 6am and closes at 11. it is open saturday and sunday. It is the "main" post office. The only problem is they are closed on holidays, including holidays on saturdays and sundays. It is always a bitter disappointment to drive up to that PO and then remember it's columbus day or something.
and you can even mail CHICKENS from there!