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24 Hour Timer
A full-day 24:00:00 countdown: press Start (or Space) and the alarm sounds after 24 hours. The ring and the end-time label show exactly when the day is up, handy for challenges, fasts from devices and dough or marinade times.
24:00:00
Ready
Presets
Shortcuts: Space start / pause · R reset · F fullscreen. Add ?m=180 to the address for a custom length. Keep this tab open; the countdown stays accurate in the background.
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How to use the 24 Hour Timer
- Press Start or hit the Space bar. The 24:00:00 countdown begins immediately.
- Want a reminder midway? Tick Soft chime at the halfway mark to hear a gentle chime at 12:00:00 left.
- Fine-tune the length with the ± buttons or pick another preset.
- Choose an alarm sound and volume, then press Play test sound to check you can hear it.
- When time is up, press Stop alarm or Space. Press R to reset to 24:00:00.
How long is 24 hour?
| Measure | 24 Hour equals |
|---|---|
| Minutes | 1440 min |
| Seconds | 86,400 s |
| Milliseconds | 86,400,000 ms |
| Hours | 24 h |
| Share of a day | 100% (1/1 of a day) |
| Walking at 5 km/h (3.1 mph) | about 120 km (75 mi) |
| Speaking at 130 words per minute | about 187,200 words |
| Reading at 230 words per minute | about 331,200 words |
What you can do in 24 hour
| Activity | Why 24 hour works |
|---|---|
| 24 hour challenge | A day without social media, sugar or complaining |
| Marinating and brining | Many marinades and brines work best overnight to a full day |
| Sourdough and cold proof | Long fermentations of 12 to 24 hours in the fridge |
| Paint and glue curing | Many products need a full day before use |
| Return windows | Keep track of a 24 hour cancellation or check-in window |
| Streak tracking | Count down to the next daily habit check-in |
How the countdown keeps exact time
When you press Start, the timer records the end moment as start time + 86,400,000 ms on the browser's monotonic clock (performance.now()). Every screen update subtracts the current time from that end moment instead of counting ticks, so a throttled background tab or a busy computer cannot make it fall behind. Pausing stores the time left, and Resume sets a new end moment that far in the future.
Frequently asked questions
How do I set a 24 hour timer?
The timer opens at 24:00:00. Press Start or the Space bar and it counts down for one full day, then the alarm rings.
How many seconds are in 24 hours?
One day is 24 hours, 1,440 minutes, 86,400 seconds or 86,400,000 milliseconds.
Will it keep running overnight?
Only while the tab stays open and the device stays awake. Computers and phones that sleep pause web pages, so keep the device plugged in with sleep turned off. The end time is shown so you know when it finishes.
Why do the buttons change by 30 minutes?
For a full-day timer, ±30 min steps are the fastest way to adjust. Use the presets (1 to 24 hours) or ?m= in the address for an exact number of minutes.
When does the halfway chime play?
If switched on, it plays once at 12:00:00 left.
Is there a longer timer?
For multi-day events, use the days until calculator or the countdown timer with a date.
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