TimerPlan12 Hours timer
12 Hours timer
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Space starts and pauses · R resets
One thing a month worth timing
MonthlyOne thing a month worth measuring or capping with a clock — a payroll trap, a nap length, a meeting that never gets added up. Two sentences and the tool.
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What is a 12 hours timer?
The Timerdial 12 hours timer is a full countdown already set to 12 hours: press start and it rings, keeps the screen awake, and shows the time left in the tab title. Twelve hours is the shift that runs hospitals and the fasting window most intermittent-fasting schedules start from. It is exactly half a day, which makes it the longest duration where the arithmetic is still obvious.
In other units that is 12:00:00 on a clock, 720 minutes, and 12 of an hour, so 0.08333 of them fit into an hour and 2 into a day.
Because the finish is stored as an absolute clock time rather than counted in ticks, the countdown is exact after a spell in a background tab, and the alarm is booked into the audio clock the moment you press start — which is what lets it sound while the tab is frozen.
Press start, or press it after changing the length — this page is the ordinary timer with 12 hours already in the box.
What people set 12 hours for
a nursing shift, an overnight cold prove, a fasting window, half a day. Twelve hours is the shift that runs hospitals and the fasting window most intermittent-fasting schedules start from. It is exactly half a day, which makes it the longest duration where the arithmetic is still obvious.
| In this unit | 12 hours is |
|---|---|
| Seconds | %!d(float64=43200) |
| Minutes | 720 |
| Hours | 12 |
| On a clock | 12:00:00 |
| Written for the box | 12h |
| Fits into an hour | 0.08333 times |
| Fits into a day | 2 times |
The address bar carries the length, so bookmarking this page keeps it, and adding ?auto=1 to the link starts the countdown as soon as it opens — useful on a shared screen where a click is one thing too many.
Next to it
Shorter: 10 hours.
Every length is listed on the timer by duration page. For a different kind of countdown, the countdown timer counts to a time of day instead of for a length, the kitchen timer runs several at once, and the pomodoro timer repeats work and break. To count upward instead, use the stopwatch.
Frequently asked questions
Should a twelve-hour timer be a browser tab?
As a display, yes; as the only alarm, no. Half a day is long enough for a machine to update, sleep or be closed, and the honest answer is that a web page cannot promise to be there at the end of it. Use it to see the count, and set the phone for the ring.
How many seconds is 12 hours?
%!d(float64=43200) seconds, which is 12:00:00 on a clock and 720 minutes as a decimal. The timer accepts every one of those forms in its box — 12h, %!d(float64=43200), 12:00:00 — and they all set the same countdown.
Will a 12 hours timer still ring if I switch tabs?
Yes. The alarm is scheduled into the audio clock at the moment you press start, so it sounds at the right time even if the tab has been frozen in the background since — unlike a page that only tries to make a sound once the time is up, by which point a throttled tab has already missed it. The remaining time is also written into the tab title and drawn into the tab icon, so you can read it without switching back.
How this works
Sources:
Reading a 12 hours countdown
It is the same engine as every timer here. Absolute finish time, scheduled alarm, screen held awake — the only difference is that 12 hours is already in the box.
The tab title carries it. So this page does not have to be the one you are looking at.
Nothing is stored. The length lives in the address bar, which is what makes a bookmark work.