He'd do way better with fins, walking along the bottom of the sea bed upright looks sloooow.
It's waaay longer than I can hold my breath, but it's nothing super-special in the world of free diving. When I lived in the UK, I was told there was freediving training you could do that trained most people to descend to 30m (90ft) and stay there for 10 seconds by the end of the day.