As I mentioned in the earlier post there are numerous stops where he can dive while others can snorkle or enjoy a beach. You might as a compromise consider having him rent 3 or even 4 tanks to minimize stops for filling tanks. That can be more disruptive to a schedule then the actual diving. He should also insure he is geared up and ready to go when you reach a dive sight. We often have all our divers in the water 5 minutes after picking up a ball and our back underway 5 minutes after the last diver is out. Non divers often can't even finish lunch if done right.
G