Should be no problem to have the divers in the water for 8 days. That close to the equator you get roughly 12 hours of daylight every day. Frequent breaks and close attention to water intake are essential. The biggest hazard we face is the temptation to push yourself too hard. The consequences are incapacitation from heat stroke or, worse, injury from fatique and carelessness.
Grave excavation is another fun activity.
Tangles of roots and big hunks of coral make for miserable digging. Our greatest concern is that someone will get hurt or sick enough to have to be evacuated, in which case we have to use the ship as an ambulance and that aborts the entire expedition. If we don't narrow things down that way we never get anywhere. He was on Tarawa when he had the bones in hand, and when he must have expressed something, somehow, that led Gallagher to think he wanted the box. However, Steenson was the actual Senior Medical Officer on Tarawa, so it seems likely that Isaac was there only in an acting capacity.