This timer runs 90-minute deep work blocks with 20-minute breaks, and a 30-minute break after the third. It follows the ultradian rhythm — the roughly 90-minute cycle of rising and falling alertness your body moves through during the day.
It is the most demanding preset here. Ninety minutes rewards hard, absorbing work, and punishes anything less, so give it your most important task and your best hours.
Who 90-minute blocks are for
Ninety minutes pays off when a problem needs to be held in your head as a whole: writing a long piece, designing a system, working through a difficult proof. Shorter blocks would force you to rebuild that mental model again and again.
It suits you less if you are interrupted often, or if your attention currently gives out well before an hour. There is no shame in starting at 50 and working up to it.
Two or three a day is plenty
Most people cannot do more than about three genuine 90-minute blocks in a day, and two is a very good day. Schedule them early, before meetings and messages fill the gaps, and use the rest of the day for shallower work.
The 20-minute break is not optional at this length. Walk, eat, get daylight. Going straight from one 90-minute block into the next is the fastest way to make the second one worthless.