You might want to do a drive by to see if there is any signage that says the ramp is closed after dark. Check out the Pennsauken Ramp or the Linden Ave ramp on the Philly side.
If that doesn't work, call one of the 2 private marinas on the Rancocas, Hawk Island or Dredge Harbor. At least you'll get a real person who can tell you if you can pick up late at night.