I just called a couple of the post offices in my area to schedule an appointment, no response. You got to wonder if they even have a phone there.
If you can't get an appointment, there is usually one in the area that has drop-in hours; no appointment needed.
For instance, there is one in Garden City, NY that you don't need an appointment.
Find out from your local post office.
Just make sure you have all your documents and photos in order and separate checks for each app. Also- fill out the application before you get there. Otherwise they'll make you come back.