> With 10C water you can only be down there for at most half an hour (especially not wearing a wet/dry suit)
He worked up to spending as long as 2 hours in the water on good days[0]:
"[I]f I've had a bad day or I haven't slept well or I've had an injury, I go in the water and it's very difficult for me to thermoregulate. If I've had a great day, I've slept well, I'm feeling strong, I can stay in for a very long time, up to two hours. But if I'm compromised mentally, I can sometimes be cold within 20 minutes."
[0] https://www.npr.org/2020/10/15/923915545/filmmaker-finds-an-...
That said, I found it a bit surprising that in his small window of time down there he managed to be at quite a few critical events in the octopus' life.