The cold plunge is a jolt, not a reset

If you like it, two to three minutes is plenty; no study has tested that dose, it's just what people do. Breathe slowly through the first thirty seconds. Don't expect it to change your brain.

3 minEvidence: decent

An hour in 14°C water sent noradrenaline up five-fold and dopamine in the blood up too, in a small group of young men; adrenaline didn't move. That's the alert, slightly high feeling people chase. Nobody has measured it the same way for a three-minute dip. Evidence: decent

What isn't shown: that any of it "resets your dopamine baseline", fixes low mood over months, or does anything the walk you'd otherwise take doesn't. The mood trials are small and short: a few dozen people, one dip, mood asked about straight after. Evidence: worth trying

Heart condition, high blood pressure, or you're on your own: give it a miss. The first minute in cold water is the dangerous one, and people drown in it. Evidence: solid

Source: Šrámek et al., 2000, European Journal of Applied Physiology (one hour at 14°C, young men); Kelly & Bird, 2022, Lifestyle Medicine (42 students, one sea dip; doi 10.1002/lim2.53); Yankouskaya et al., 2023, Biology (33 people, 5 min at 20°C; doi 10.3390/biology12020211); Tipton et al., 2017, Experimental Physiology (cold shock review; doi 10.1113/EP086283) (link)

Same theme: Through the day

Through the day
Hard work at your best hour
Notice when your head is sharpest. Put the hardest task there. Admin goes in the slump.
no timeEvidence: decent
Through the day
Move for the tiredness
Too tired to train? Go anyway, and go easy, at a pace you could talk at. Three times a week for six weeks, then judge.
3x a weekEvidence: decent
Through the day
Stairs before the coffee
Afternoon slump? Walk up and down the stairs for ten minutes before you buy the coffee. Then decide if you still want it.
10 minEvidence: worth trying