How long to cold plunge has no single answer, because time and temperature trade against each other: three minutes at fifty degrees and eight minutes at sixty are roughly comparable exposures. What follows is what the research protocols actually use and where the limits sit, rather than a number someone picked for a video.
What the protocols use
Studies on cold water immersion for muscle soreness generally use somewhere between five and fifteen minutes at temperatures in the high forties to low sixties Fahrenheit. Colder water shortens the useful time. Nothing in that literature supports the idea that longer is better, and the discomfort rises much faster than any measured benefit does.
A sensible way to build up
Start at the warm end and a short duration, perhaps a minute or two, and lengthen before you go colder. The first thirty seconds are the hardest part in any water below about sixty, because of the involuntary gasp and the spike in heart rate. Getting that under control is the skill, and it comes with repetition rather than duration.
The limits that matter
Shivering that continues after you are out and dressed means you went too long or too cold. Numb hands and feet, or difficulty with fine movements, are a stop signal. Never plunge alone, never after alcohol, and get out at once if you feel lightheaded. Cold shock, not hypothermia, is what hurts people in short home sessions.
After a workout
If you lift, the timing matters more than the duration. Immersion immediately after resistance training has been shown in several studies to blunt some of the adaptation you trained for. If strength is the goal, put the plunge on a rest day or several hours later. For general recovery from endurance work the concern is much weaker.
Questions people ask about how long to cold plunge
Is three minutes the right number?
It is a reasonable target at around fifty degrees, but it is a convention rather than a finding. Warmer water supports longer, colder water shorter.
How often should you do it?
Most people who keep it up settle at two to four times a week. Daily is not shown to be better and makes the habit harder to sustain.
Should you warm up straight afterwards?
Warming passively with clothes and movement is fine. Jumping into a hot shower immediately undoes much of the point, and a sauna straight after is a large swing to put on your heart.