90/20 deep work timer
one long block for deep work, then twenty minutes away.
who 90/20 suits
ninety minutes is a block for work that needs a long runway: a big refactor, a long essay, a design problem with lots of moving parts, or a full practice paper. the length is usually linked to the sleep researcher Nathaniel Kleitman's basic rest-activity cycle, the idea that alertness rises and falls in roughly 90 minute waves. using it as a work rule rests more on people's own experience than on firm proof, so it is worth testing rather than trusting.
it works best when you can protect the whole block. close messages, put your phone in another room and decide on one task before you press play. the twenty minute break matters as much as the block itself, so step away from the screen completely.
if you have ADHD or simply drift after half an hour, ninety minutes may be too long to start with, and that is fine. our post on 90-minute work blocks covers the evidence and how to build up to it.