When a session ends itself, and why the clock runs backwards

The failure this fixes is boring and universal. You finish, you towel off, you talk to someone, you drive home, and four hours later your watch is still timing a sauna session. The old record says 4 hours 12 minutes. The true answer was 48.

Three ways a session ends

You end it. The last page of the running session on the watch is a single End button in the middle of the screen, on its own page so it cannot be hit by accident while you are reading the totals.

A long rest ends it. After five minutes with no round running, the session closes by itself. The default is five minutes; the setting accepts anything from one minute to three hours.

A very long round ends it. A single round that runs past 90 minutes closes the session too. Nobody sits in a sauna for an hour and a half, so a round that long is a round nobody closed.

The back-dating, which is the whole point

An auto-end that stamped the end time at the moment the timeout fired would record five minutes of phantom rest on every session, and far more than that when the trigger was the 90-minute round cap.

So the end time is not the moment the timer noticed. It is the moment you actually stopped — the end of the last real segment, the last time you were in water or moving between rounds. The timeout decides that the session is over; the timeline decides when.

The difference on a normal session is five minutes. The difference on a session you walked away from entirely is the whole afternoon.

The countdown you see first

Before any of that, there is a smaller prompt. When your wrist leaves the water, the watch asks out of water? with a 30-second countdown and two answers: I’m out, which closes the round and does what Switch would, and still in, which cancels the question.

That prompt is about the round rather than the session, and it has the same back-dating property: the round closes at the moment you left the water, not at the moment you answered. Ignoring the question entirely is a valid way to use it, which is the point — the default answer is the correct one.

If the session is close to ending itself, page one of the watch shows a small hourglass and a countdown in the corner where readiness usually sits. Tapping it says still going and buys another ten minutes against the round cap.

Why five minutes

Rest between rounds is a timed segment in Contrast rather than a gap, and a real contrast session has several of them. Two to three minutes between a sauna round and a plunge is ordinary. Five minutes sitting on a bench before going back in is ordinary. Fifteen is not.

Five minutes is short enough to catch a session you abandoned within the same visit and long enough that a genuinely leisurely rest is not cut off. Anyone whose routine includes a longer break has the setting, and the range runs to three hours for the person doing a full afternoon.

The cost of getting this wrong in either direction is asymmetric, which is worth saying because it explains the default. A timeout that is too long records a session that ran too far, and you notice it and edit it. A timeout that is too short splits one session into two, and you may never notice — the totals are right and the session count is wrong, which quietly distorts the sessions-per-week figure the cohort comparison uses.

What happens to the Health workout

The workout written to Apple Health carries the corrected end time, not the timeout. A session that auto-ended after you left records the duration you actually did, and your other apps see that.

If you do end up with a session that ran long — a genuinely forgotten watch, or a timeout set too generously — you can trim it on the iPhone afterwards. Editing a session recomputes its stats from the samples inside the new bounds rather than scaling the old numbers, so the heart rate average after a trim is the average of the part you kept.

Water Lock, and why this design exists at all

Getting into water turns Water Lock on. That protects the screen from splashes, and it also means that for the duration of the round you are not going to be operating the watch.

An interface you cannot touch has to be one you do not need to touch. Every automatic behaviour in the app comes from that constraint: the round that starts itself on submersion, the round that closes when you climb out, the prompt whose default answer is right, and the session that ends when you have plainly stopped.

The one thing a person has to do is get in the water.