it is supposedly 2 hours descent - 5/6 hours looking around the shipwreck - and then a 2 hour ascent back up.I don't think they are. In fact, I'm sure they're not. I believe the descent takes a good few hours, then presumably they nose around for a couple of hours, then start the ascent, which takes another good few hours. That's it.
In normal circumstances that is. this is obviously abnormal.