The 90-minute focus timer is built on the ultradian rhythm — the body's natural ~90-minute cycle of attention, alertness, and fatigue first mapped by sleep researcher Nathan Kleitman and later applied to waking performance by Anders Ericsson and Tony Schwartz. Unlike the 25-minute Pomodoro (which is shorter than most cognitive warm-ups) or the open-ended "just keep going" approach (which ignores how attention actually decays), 90/20 matches what your brain is already doing whether you notice or not.
This free timer is intentionally minimal: a 90-minute focus countdown, a 20-minute recovery break, a 3-cycle daily ceiling, and a soft audio chime when each phase ends. No accounts, no syncing, no analytics dashboard — your cycle count resets at local midnight and lives only in this browser. The whole tool is one file and works offline once loaded.
Why 90 minutes and not 25 or 50:
- Most knowledge work has a 15–20 minute warm-up phase before flow even becomes possible — you spend the entirety of a 25-min Pomodoro just clearing the runway.
- The ultradian peak sits between roughly minute 30 and minute 75 of a focused block. A 90-minute container gives you the full peak plus enough overhang to finish the thought instead of cutting it mid-paragraph.
- After ~90 minutes, prefrontal glucose drops measurably and error rate climbs. Pushing past the bell is how you produce hours of mediocre work and call it "grinding."
Why 20 minutes for the break, specifically:
A 5-minute break is a glance at your phone — it doesn't recover anything, it just task-switches your attention into something more dopaminergic and then expects it to come back. 20 minutes is the minimum window for actual recovery: a real walk, real food, real conversation, real staring at a wall. The break is not a reward for the focus block; the break is *part of* the focus block. Without it, the next cycle is degraded.
Why 3 cycles is a strong day, not a weak one:
3 × 90 minutes = 4.5 hours of genuine deep work. Most knowledge workers ship less than 2 hours of real focused output per day; if you reliably hit three full ultradian cycles, you are at the 90th percentile of working scientists, writers, and senior engineers. Stop after the third. The fourth is where errors and burnout enter.
How to actually use it:
Pick one task before you press start — not "work on the project," a specific deliverable you can finish or meaningfully advance in 90 minutes. Phone in another room. One tab. Water nearby. Press start, do the work, stop when the chime rings even if you're flowing — that discipline is what makes you trust the tool tomorrow. Take the full 20-minute break away from the screen. Repeat up to three times.
When this won't work:
If your day is meeting-heavy, you won't get three uninterrupted 90s and that's fine — defend one and call it a win. If you're in a maker role (engineering, writing, design) and your calendar still won't yield three 90s, the calendar is the problem, not the timer. For chronic inability to start, pair this with the Task Paralysis Helper — start a 90 only once you've cleared the activation barrier.
If you want this same rhythm tracked across days with billable-hour logging, calendar sync, and a real session history, that's the LemTask focus timer inside the main app. For a one-tab, no-signup ultradian timer that just works, this is enough.