Deep Work Timer: 90 minutes focus, 20 minutes rest

Deep work is a term popularized by computer science professor Cal Newport in his book "Deep Work": professional activity done in distraction-free concentration that pushes your cognitive abilities to their limit and produces work that is valuable and hard to replicate. Its opposite is shallow work, such as email, scheduling and quick messages, which can be done while distracted.

Newport argues that this ability is becoming both rarer and more valuable. The practical takeaway: protect long, uninterrupted blocks for your most important work, and treat them as seriously as a meeting.

The 90-minute length is linked to ultradian rhythms, biological cycles that repeat several times a day. Sleep researcher Nathaniel Kleitman proposed a "basic rest-activity cycle" of roughly 90 minutes that shapes our sleep stages and, he suggested, continues during waking hours as well.

The theory is that alertness rises and falls in waves, and that resting at the low point of a cycle works better than pushing through. Evidence for daytime cycles is less clear-cut than for sleep, so treat 90 minutes as a starting point rather than a law. Many people find it matches the moment their attention naturally starts to fade.

Ninety minutes is a long time to hold attention, especially if you are used to checking your phone every few minutes. If the first sessions feel exhausting, start with 50/10 or 52/17 and build up. Both are in the preset menu under the timer, and you can set any custom length in the settings.

The 90/20 rhythm works best for creative and analytical tasks with a long ramp-up, such as writing, research, programming or studying complex material. In reactive jobs where you must answer people quickly, one protected deep work block per day is already a big win.