How long should you stay in an ice bath depends almost entirely on how cold the water is, which is why a single number is never a good answer. What is consistent across the research is that the useful exposures are short, and that longer has never been shown to be better.
Duration by temperature
In the high fifties to low sixties, ten to fifteen minutes is comfortable and is where many study protocols sit. In the low fifties, five to ten. Below fifty, most people are looking at two to five minutes and the discomfort is the limiting factor rather than any physiological target. The colder it is, the shorter it should be.
Building up
Lengthen before you go colder. The first thirty seconds in any genuinely cold water are the hardest because of the gasp response and the spike in heart rate, and learning to breathe through that is the skill. Once you can enter calmly at a moderate temperature, adding a degree of cold is easier than adding a minute of time.
The signals to stop
Get out if you start shivering hard, if your hands or feet go numb enough that fine movement is difficult, or if you feel lightheaded. Shivering that continues after you are dressed means the session was too long or too cold. None of these are things to push through: the benefit does not increase past the point of comfort but the risk does.
Afterwards
Warm up passively with clothes and gentle movement rather than a hot shower, which undoes much of the point and can make you feel faint as vessels open quickly. Give it fifteen minutes before driving. And never plunge alone while you are still learning what your own limit feels like.
Questions people ask about how long should you stay in an ice Bath
Is three minutes the standard?
It is a reasonable target around fifty degrees, but it is a convention rather than a finding. Warmer water supports longer and colder water much shorter.
Does longer give more benefit?
No. Nothing in the research supports extending past the protocol durations, and the risk of getting cold enough to matter rises.
Should I have a hot shower after?
Better to warm up gradually. A hot shower straight after can make you lightheaded as blood vessels open quickly.