I think I've done about 90 minutes in one dive (i.e. Not going shallower than 5 metres). I start getting cold then, and that's just not fun!

Those guys were technically doing multiple dives over 5 hours rather than one five hour dive, I think?

The divers in the video were very competent ..... you can tell by their horizontal position in the water and the way they kick, it's a different technique to open water diving as it doesn't stir up silt.