Why 25 Minutes Is Not Enough: The Ultradian Rhythm Timer
The 25-minute timer is a good tool for starting. It can be a poor tool for staying in the work. Just as the friction of starting fades and your attention settles, the bell rings and forces you to stop.
Most focus apps assume attention is linear. You push a button, you work for a set period, you rest for five minutes, and you repeat until the day is done. Attention does not always work that way. There is good reason to think it moves in longer waves.
The 90-minute cycle
Nathaniel Kleitman proposed the basic rest-activity cycle in the 1950s. He observed that the brain moves through roughly 90-minute periods during sleep, alternating between distinct stages. The idea that a similar cycle governs daytime alertness — stretches of high focus followed by a dip — is a popular extension of that work, though the daytime evidence is thinner and more debated than the original sleep research.
Whatever the exact length, the practical point holds: when you force a 25-minute grid over attention that wants to run longer, you create friction. You stop when you should be accelerating.
The cost of manufactured interruptions
Getting into a state of flow takes time. For ADHD brains, the executive function cost of task initiation is often the highest hurdle of the day. Once you cross that hurdle, your attention becomes a valuable and fragile resource.
A strict Pomodoro timer can manufacture an interruption right as that resource peaks. Interruption research suggests that recovering from a break in attention costs more than the break itself. A tool that demands you stop every 25 minutes may be charging you a recovery tax several times an hour.
The deepstint approach
deepstint does not lock you to 25 minutes. Sessions are configurable, so you can size the container to the work in front of you.
- Set the timer for 90 minutes to hold deep work without an artificial cutoff.
- Take a longer rest block afterward to allow real recovery.
- Use the "Keep going" button to extend any standard stint without breaking flow.
The goal is not to trap you at your desk for an hour and a half. The goal is to provide a container large enough to hold deep work without artificially cutting it short. If you finish the task in forty minutes, you stop the timer. The record logs the exact time spent.
You do not have to fight your own rhythm to get work done. You just need a tool that gets out of the way.
Design principle: protect focus.
Try deepstint today. Start a stint, hit your stride, and hit "Keep going" when the timer rings.
References
Kleitman, N. (1982). Basic rest-activity cycle—22 years later. Sleep, 5(4), 311-317.
Mark, G., Gudith, D., & Klocke, U. (2008). The cost of interrupted work: more speed and stress. CHI 2008 Proceedings.
Read more about the design logic in why deepstint works this way.
Common questions
What is an ultradian rhythm?
An ultradian rhythm is a biological cycle that repeats more than once a day. In the context of focus, people often point to roughly 90-minute periods of higher mental alertness followed by a stretch of lower capacity. The daytime version of this is less settled than the sleep research it draws from.
Why can 25 minutes feel too short for deep work?
Task initiation has a high cognitive cost. By the time you overcome the friction of starting and settle into the work, a 25-minute timer can force you to stop — manufacturing an interruption right as you hit your stride.
How do you use deepstint for 90-minute focus blocks?
deepstint sessions are configurable, so you can set the timer to 90 minutes and take a longer break afterward. You can also use the keep going feature to extend a standard session into a longer block without stopping the clock.