Its like asking how heavy weights should I lift at the gym?' Well it depends. Is it your first time? Whats your body mass? And for the ice bath; what's your body's thermogensis like? What temperature is the water? (By the way the most underrated question!).

There is no size fits all. Maybe the first time you just look at the ice bath and that brings enough anxiety for one day. Maybe the next time you think about actually going in. Maybe on the 5th night of the fourth moon you've had a dream where a wizard gives you a snow flake and you wake up knowing you're ready to go inside. Maybe you jump in and out in 1 second. That's great! Maybe the next day you do the same thing but at least you know what to expect. By day 75 you're sitting in the chest freezer like a zen monk for 15 seconds before you clamber out in such pain, agony and regret its only after another 97 sleeps that the wonderful wave of clarity and euphoria you experience for the following 5 hours you begin to understand why it's so addictive.

Build up your time slowly and don't push yourself, otherwise you'll build up so much resentment towards the ice bath that after a few months it will just be something you 'use to do' like waking up early to pack a salad for work.