15 Hour Timer
Free online 15 hour timer with alarm. Set a 15-hour countdown for long tasks.
⏱️ 15 Hour Timer: Start a free 15-hour countdown timer instantly — no downloads, no sign-up. Just click Start.
Why use a 15-hour timer?
A 900-minute timer is useful when standard intervals (Pomodoro 25, ultradian 90, NASA nap 26) don't quite match your task. Longer than the standard 120-minute deep block.
What people use a 15-hour timer for
Multi-block deep work
900-minute typically requires breaking into 2 sub-blocks with a break between.
Extended training
Marathon and endurance training routines run in this 900-minute range.
Tabletop RPG session
D&D, Pathfinder, and similar typically run 2-4 hours per session.
Long exam
LSAT, MCAT sections, full bar exam blocks reach this 900-minute.
Theatrical production
Movies, plays, operas — full performance lengths.
The 15-hour interval, in context
900-minute exceeds standard single-block focus capacity for most people. Optimal use: split into sub-blocks separated by breaks, per Anders Ericsson's deliberate-practice research.
Longer than the standard 120-minute deep block.
About the 15 Hour Timer
Free online 15 hour timer with alarm. Set a 15-hour countdown for long tasks.
Related
Frequently asked questions
Why use a 15-hour timer specifically?
15-hour sessions are for extended-focus work, multi-section practice exams, slow-cook recipes, and long meditation retreats. For very long timers, keep the page in the foreground tab — modern browsers may throttle background scripts after extended periods.
Does the 15-hour timer keep accurate time?
For 15-hour intervals, accuracy is typically within 1 second across the full window when the tab stays open. If you minimize the browser for hours, some operating systems aggressively throttle background tabs — keep the tab visible if exact end-time matters for cooking or testing.
Should I keep this timer running for a full 15-hour session?
Yes — keep the tab open and visible for the full 15-hour. Modern browsers throttle background tabs aggressively, especially on battery-powered devices, which can delay the alarm or cause inaccurate end times. Pin the tab if you need to switch away briefly.
What happens when the 15-hour timer reaches zero?
An audible alarm plays and the page flashes a completion indicator. After a 15-hour session, you have probably switched contexts entirely — make sure your device is on a surface where you can hear it, since the alarm is your only return signal.