A 90 minute timer aligns with the brain's natural ultradian rhythm — the ~90-minute cycle of alertness and recovery identified by sleep researcher Nathaniel Kleitman. Neuroscientist Andrew Huberman recommends structuring deep work in 90-minute blocks to match peak cognitive performance windows. It's also the exact length of a soccer half, a typical feature film, and a standard university lecture.
Enable Repeat to automatically restart the countdown — perfect for interval training or back-to-back sessions. Enable End Time to see the exact clock time your timer will finish.
Click the Countdown tab, type 1 in the hours field and 30 in the minutes field, then press play or Space. The alarm plays when your 90-minute countdown reaches zero.
The ultradian rhythm — a ~90-minute cycle of heightened focus followed by a rest phase — was identified by sleep researcher Nathaniel Kleitman. Andrew Huberman's neuroscience research recommends aligning deep work blocks to this cycle: 90 minutes of focused work followed by a 20-minute break for full recovery.
Yes. Click the PiP button to float the timer above all other windows. Your 90-minute countdown stays visible while you write, code, or research — no tab switching needed. Available on Chrome 116+ and Chromium-based browsers.
Yes. Enable the End Time toggle before starting. Polytimer displays the exact clock time your session will finish — e.g., "Ends at 4:30 PM" — so you can plan your day without watching the clock.