90-minute focus timer

Where the 90-minute idea comes from

Most "work in 90-minute blocks" advice traces back to Nathaniel Kleitman, the sleep researcher who described the roughly 90-minute cycle of sleep stages. He proposed that a similar basic rest-activity cycle runs through the waking day as well (Sleep and Wakefulness, 1963).

The waking half of that idea has always been argued over. Kripke and colleagues published a paper in 1977 titled, bluntly, "There's no basic rest-activity cycle"; later work by Peretz Lavie (1992) found ultradian rhythms in how sleepy people get during the day. A readable summary with all three references is the Wikipedia article on the basic rest-activity cycle. None of it shows that 90 minutes is the best length for a block of work.

What 90 minutes does give you is room. Some work can't be done in pieces: debugging something with a lot of moving parts, drafting a long section in one pass, a practice exam under real conditions. For those, being interrupted at minute 25 costs more than the break gives back.

What 90 minutes looks like

The squares are smaller than in a 25-minute block, but the shape still tells you where you are. After an hour, six of the nine rows are hollow.

A four-hour afternoon at 90/20

Two blocks make an afternoon: 180 minutes of focus with a single break between them. The 50/10 timer fits 200 minutes into the same four hours, but in four pieces. The long block is also the least forgiving: if the second block starts badly, there's no fresh start until 4:20.

Setting it up in the app

In Pomo, open Settings, then Session, and set Focus to 90 (it goes up to 120) and Short break to 20. If a 90-minute block is a one-off, leave your defaults alone and drag the face up on the timer screen before you begin. Pomo also keeps the screen awake while a session runs, which matters more over 90 minutes than over 25; you can turn that off in the same Session settings.

By the Pomo team