How do I set a 21 hours timer?

Click the Start button to begin the countdown. You can adjust time with +1m/-1m buttons or click the display to set a custom time.

What happens when the 21 hours timer ends?

The timer plays an audio alert and can show a notification (if enabled). Enable Repeat mode for continuous intervals.

21 Hours Timer — Free Online Timer (Works Offline)

21:00:00

Set Timer for Specified Time

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1 Minute Timer 2 Minutes Timer 3 Minutes Timer 5 Minutes Timer 10 Minutes Timer 15 Minutes Timer 20 Minutes Timer 25 Minutes Timer 30 Minutes Timer 35 Minutes Timer 40 Minutes Timer 45 Minutes Timer 50 Minutes Timer 60 Minutes Timer 90 Minutes Timer

1 Hour Timer 2 Hours Timer 3 Hours Timer 4 Hours Timer 5 Hours Timer 6 Hours Timer 7 Hours Timer 8 Hours Timer 9 Hours Timer 10 Hours Timer 12 Hours Timer 18 Hours Timer 24 Hours Timer 48 Hours Timer 72 Hours Timer

About 21 Hours Timer

Set a 21 Hours countdown timer for free. This online timer works offline as a PWA, supports audio alerts, keyboard shortcuts, and repeat mode.

How to use

Click the Start button to begin the countdown. Use +1m/−1m buttons to adjust time quickly, or click the timer display to set a custom duration. Press Space to pause/resume, R to reset, and F for fullscreen.

Features

Works completely offline after first load (PWA)
Multiple timers (add with the + button)
Fullscreen mode for presentations and classrooms
Repeat mode for continuous intervals
Browser notifications (with permission)

Use cases for 21 Hours

Full work day
Overnight timers
Server maintenance windows
Hackathons
Exam supervision

Tips for using this timer

Press Space to start/pause
Press R to reset timer
Press F for fullscreen mode
Click the + button to add multiple timers
Enable Repeat mode for continuous intervals

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