There are no set hours - other than between dawn and dusk. You just show up, pay at the office, sign a release and hand over coggins and be on your way. We were there this week and while I enjoy Fair Hill, since it was just myself and my trainer (usually she brings several students), it was nice to have the place to ourselves and not 'wait in line'. The fee is $20/horse.
Actually, the office is often not open when I've been there, but you can leave the release, copy coggins, and check in an envelope there on the office door, or give it to a manager at the barn around where you park.