I don't know about the Admiral's Club in SAN specifically, but I doubt very much that it is a 24hr operation. To be frank, I think you are being a little cheap. It would help if you could elaborate on your origin and destination, but I would always opt for a hotel room for an 8 hour layover. Pick up your bags (you may be able to recheck them, I have in these instances, though not specifically at SAN), and get a decent night's sleep at an airport hotel.