That totally depends on Customs. One cruise, they didn't start disembarking until after 10 am and we were there before 7 am. Once you do get off the ship, you have to collect your luggage. I've never sailed from San Juan, but in Fort Lauderdale, the luggage is put in a large room, with color tags on the walls overhead. It can take quite awhile to find yous (expecially if it's a black suitcase). On the Coral, we were held up at this point because the dogs were finding lots of cuban cigars and customs had to check many bags. There was quite a bottleneck getting out of there that day.
Best bet is to get a noon or later flight. You're really taking a chance getting something earlier. If you do book an earlier flight and miss it, good luck getting on a later flight. So many cruisers dump into the airport that the flights seem to always be overbooked.
Good luck!
