Shit... I haven't done anything that long! I reckon 30min at 10min would feel fine. I do 5min at 5°c every day and the max I've done is 10min at 5°c which was enough for me...freaks me out after that my HR goes down to 48bpm lol
Discussion
I find that my tolerance for time goes up a lot at the higher temperatures. Been playing with that as I’m also looking at the ice bath as an alternative way to meditate.
Have you heard of the 12hour challenge? If not you should listen to it on Joe Rogan with Colin O'brady(great episode). I'm yet to try it but it is on my list of things to do. Basically go for a 12hr walk and disconnect, no music, podcast etc. Be alone with your thoughts for 12 hours apparently it can get you into an extreme meditative state.