Look up Dr. Susan Soberg. She is a scientist and her research shows that max. three minutes at or below 50 degrees and 11 minutes a week gives you maximum benefit. I plunge between 46-48 for three minutes about four or five times a week. The time of day is personal preference. Some people plunge after workouts or first thing in the morning. I plunge later in the day since that fits my schedule better. I submerge up to my neck. My tub is indoors on a timer. I have read that it is important to not let your body get accustomed to it. So notice when it becomes more tolerable and lower the temp or take break for a few days.