ADHD and the 25-minute timer: why one length doesn't fit every brain

The number 25 gets treated like it came from a lab. It didn’t — Francesco Cirillo picked it because that’s what his kitchen timer happened to be shaped like, a tomato, sold in 25-minute-ish twists. There is no study saying 25 minutes is the correct duration for a human brain, ADHD or otherwise, and treating it as gospel is why a lot of people quietly conclude the whole technique “doesn’t work for them” when the real mismatch is much smaller than that.

Where 25 actually comes from

It’s worth saying plainly: the number is arbitrary. What isn’t arbitrary is the idea underneath it — bounded blocks with a hard, audible end — which is the part that matters for time blindness and for getting started at all. The 25 is a starting guess, not a diagnosis of how your attention actually behaves.

What attention research actually says about duration

Sustained-attention research generally finds two things worth knowing here. First, attention lapses can begin surprisingly early on a task — some studies put the first lapses as early as 8 to 10 minutes in, with more consistent performance decline setting in around the 20–25 minute mark for many people. Second, and separately, the body runs on a much longer natural cycle: sleep researcher Nathaniel Kleitman first documented an ultradian rhythm of roughly 90–120 minutes of alertness, later validated in laboratory work by Peretz Lavie, whose findings pointed to something closer to 75–125 minutes of natural focus capacity before a real dip. Individual variation inside that range runs 15–30 minutes wide.

Put those two findings next to each other and 25 minutes looks less like a number and more like a compromise between “attention degrades early” and “the body wants a much longer cycle” — which is exactly why no single length is going to fit everyone.

Finding	What it suggests for session length
Attention lapses can start at 8–10 minutes on some tasks	A shorter block may suit tasks that are naturally low-stimulation
Consistent decline often sets in near 20–25 minutes	The classic Pomodoro length sits right at this edge, not comfortably inside it
Natural ultradian focus cycles run ~75–125 minutes	Some people genuinely do better with fewer, longer blocks than four short ones
Individual variation is 15–30 minutes wide	“Standard” length is a starting guess, not a fit

Finding your actual number

The practical version of all this: treat 25 as a first guess, not a commitment. If you consistently feel finished before the bell, try 15. If the bell keeps interrupting something that had just started working, try 40 or 50. PetPomo’s duration is adjustable in Settings for exactly this reason — the countdown and the sleeping cat work the same at any length, because the mechanism that helps isn’t the specific number, it’s having a visible, external, bounded block at all.

There’s a reasonable, mixed answer to whether the technique as a whole is actually backed by evidence — worth reading before deciding the method itself is wrong for you, rather than just the number attached to it.

PetPomo is a timer, not a treatment. Nothing here is medical advice — if attention or focus is a real, ongoing struggle, a doctor or specialist is the right person to talk to.