[ He gives a small laugh. He doesn't want to use his bubble charm either, but he will be helpless once he hits the water. This gives him more of a chance to be saved by increasing the time someone else has to save him. He could still drown should be be alone, but that would be the case without the charm. ]

I believe it is two hours per go. Nothing suggested it was a one-time use, and the other charms I have allow for multiple uses.