It's maybe 2-something hours to the Palm Beach/ Martin county line and Jupiter Dive Charters. Key Largo is another few hours south - you have to drive through the length of Dade and Broward counties, home to some of THE most brain-dead drivers anywhere and then traverse the US1 Highway of Death between Florida City and Key Largo. Yes, I know that you can take the toll road around Card Sound, but it's longer and boring. Still, if the Highway of Death is shut for yet another Medevac, this is how you will gratefully go.
There's good diving in the Keys - Spiegel Grove, Duane, Bibb - but that's a long drive from Orlando and then you have to go north again after that all the way back to Mouseville.