I've also been scuba diving once, lol. This rescue is definitely complicated enough, but at least there will be areas of above water swimming and three or four dry areas where they could take a break. But three hours of underwater swimming is treacherous in murky water.
But these boys are soccer players and, er, cave explorers, so they have done physically demanding things in their young lives and that is a reason for optimism. They're not a bunch of couch potatoes and computer gamers who live indoors all the time.
So there should be news of the rescues mid-morning tomorrow. Thai time is exactly 12 hours ahead of CDT.