Can it really do 15-second rounds, like the shopper asked?

Yes. The number you type is the length you get: 15 makes a fifteen-second round, 35 makes a thirty-five-second one. Uncommon values are not special cases anywhere in the setup.

Are half-second or decimal intervals possible?

No. Whole seconds are the finest step. Interval protocols themselves are written in whole seconds, so a decimal on a printed sheet is really an instruction to round.

Will I have to retype my odd scheme before every session?

No. You build the scheme once and it becomes a named preset, started like any other from then on. Naming it after the numbers, 35/25 x 8, keeps the phone and the sheet in agreement.

Why do so many timers stick to 30/45/60 presets?

A short grid covers the protocols people search for, and it costs less to ship than free-text duration fields with validation. The arrangement works for a while. Then a plan shows up with 35 seconds in it and nowhere to put them.

Odd intervals: 35/25, 50/10 and the 15-second question

On a boxing subreddit, someone shopping for a timer put their two deciding questions in one breath:

“Does it interfere with music playing on my phone? Can you adjust round times to 15 second intervals? If so I’m sold.” (r/Boxing, 2026)

The music half of that question is answered in a separate piece. This one is about the number half, which reads like a niche ask and works like a purchase condition: fifteen-second rounds, thirty-five on and twenty-five off, whatever the plan in front of you says. If the timer cannot hold numbers like those, it cannot run the session you planned.

The numbers training runs on

Preset grids ship the hits: 20/10 for Tabata, 30/30, a minute on and a minute off. Plenty of real programming sits elsewhere. A standard warm-up ladder is four rounds of 45 seconds easy and 15 building. Repeaters for climbers run seven hangs of ten seconds with five off, and on harder edges the hang itself drops to seven. The rest between two stations in a circuit lands around fifteen seconds, because that is what the walk takes.

Each of those numbers came from somewhere outside a timer: a warm-up protocol, a sport’s standard practice, the length of a walk across a room. Fartlek goes further and picks durations by feel mid-run, odd by construction. A sheet that reads 35/25 or 50/10 is more of the same: ordinary numbers, written down by somebody for a reason.

What rounding does to a session

When your number is missing from the grid, the reasonable move is to round: thirty-five up to forty. The session on the clock is then no longer quite the session on the page. Take two schemes: 2:00 on with 1:00 off, and 2:15 on with 0:45 off. Both cycle in three minutes. One runs at 2:1, the other at 3:1. They are different workouts. The time on the clock barely moves. What you asked of yourself does not. Rest answers to that arithmetic too; rest between rounds gets a full article.

Granularity is a programming variable

Everyone expects three fields: work, rest, rounds. Alongside them sits a fourth variable: the step of numbers the fields will accept. Store screenshots tend to bury it in an advanced-settings tab.

The odd numbers usually arrive second-hand. A physio’s sheet after an injury says 50 on, 10 off; the off-season block comes by email from a coach who has never seen your phone. A timer that accepts any whole-second value meets them there.

The fifteen-second question, answered

Work, rest and round lengths are typed as durations, in whole seconds, from one second up to an hour. A fifteen-second round goes into its field exactly the way a three-minute one does. For the days when the standard grid is enough, presets like 20/10 sit one tap away.

Where Intertakt stands

In Intertakt, every duration field takes a typed whole-second value, from 1 to 3600. A 35/25 scheme saves as a preset and sits in the list next to the 20/10s. How presets get built is covered in an earlier post. Intertakt is out on Google Play. If you want one email when the iOS version lands, leave your address on the waitlist.