Do 90-minute work blocks work? Check your own sessions on a Mac

9 October 2026 · 6 min read

Ninety-minute work blocks suit some people and not others, and your Mac can tell you which group you are in. Run a two-week test: one week as usual, one week with a protected 90-minute block each day. Then compare how much unbroken time your main working app actually got, rather than how productive the week felt.

What a 90-minute block is supposed to do

The idea is popular in productivity writing: work on one demanding thing for about ninety minutes, with nothing else allowed in, then take a real break before the next block. The block is meant to be long enough to get past the warm-up, when you are still loading the problem into your head, and short enough that you can hold attention all the way through.

You will find confident claims about why ninety minutes is the right number. You do not need to settle that debate to find out whether the format helps you. Your own week is better evidence than a general rule, and it is the only evidence that applies to your work, your interruptions and your energy.

What your Mac can measure, and what it cannot

Your Mac knows which app is in front, from moment to moment. That turns out to be a useful proxy for a work block.

What it can show:

How long your main app stayed in front without a break. If you write in a word processor or code in an editor, a long unbroken stretch in that app is a block that held.
How often you left. A block interrupted by a forty-second look at chat shows up as two sessions in the editor with a short chat session between them.
When in the day the long stretches happened.

What it cannot show:

Whether you were concentrating. An hour in the editor can be an hour of staring.
Thinking away from the screen. Sketching on paper or pacing the room does not register as app time.
Output. How much got done is something you judge yourself.

So the Mac gives you the structure of the day, and you add the judgment. That is enough for a fair test.

Set up a two-week test

Keep it simple, and keep the two weeks as similar as you can.

Week one: change nothing. Work as you normally do. This is your baseline, and it matters more than it seems: it is hard to judge a change without a clear picture of the ordinary day.
Week two: add one block a day. Pick a fixed time, ideally the part of the day you are least likely to be needed. Choose the one task for the block before it starts.
Protect the block. Close chat and mail, not just minimize them. Turn on a Focus from Control Center so notifications wait. Put the phone in another room.
Take a real break afterward. Stand up and step away from the Mac for at least ten minutes. The break is part of the format, not a reward for finishing.
Write one line a day. Did the block happen? What did you get done in it? Thirty seconds at the end of the day.

Avoid comparing a week of deadlines with a quiet week. If your work has a monthly rhythm, run the test across two ordinary weeks rather than the two most convenient ones.

Read the result

You need a record of both weeks that you did not have to keep by hand, because a test that depends on starting and stopping a timer measures how good you are at remembering the timer.

Punchcard keeps that record on its own. It notices which app is in front, app names only, and at the closing time you set it prints a receipt of the day: the top five apps with time on each, the rest as MISC, and a day total. On Sunday it prints a week roll. Put the two Sunday rolls side by side and look at three things:

Your main app’s share of the day. Did it grow in the block week, or did the same hours just move earlier?
The size of MISC. Lots of short visits to many apps pile up there. A smaller MISC in the block week means less scatter.
The day total. If the total went up, check whether the block added focused time or simply added hours.

For a closer look, export the CSV. It has one row per session, with a start, an end, the app and the seconds. Open it in Numbers, filter to your main app, and sort by seconds:

Longest session each day. In a baseline week, this might be twenty minutes. If the block week shows sessions near an hour or more, the block is holding.
Sessions over twenty minutes. Count them per day. More long sessions means more real stretches of work.
Very short sessions in other apps. Count the ones under two minutes during your block time. Those are the glances that break a block into pieces.

Then read your one-line notes. If the numbers improved and the notes say you got more done, the format works for you. If the numbers improved but the notes do not, you got longer sessions without better work, which points to the wrong task in the block rather than the wrong format.

If you want to go further with the CSV, Export your time data to CSV and keep it forever covers opening and storing it. Tracking is free and never expires, the CSV export works without a license, and the first two receipts are free.

If ninety minutes is wrong for you

A failed test is still a result. Common adjustments:

Shorter blocks. If your longest session kept breaking around forty minutes, try forty-five-minute blocks and see whether they hold every time.
Two blocks instead of one. Some people get a solid morning block and a weaker afternoon one. The record shows which time of day holds better; How to find your most productive hours goes deeper on that.
A different task. Blocks work best for work that needs a warm-up: writing, design, code, analysis. They are wasted on email.

If a timed cycle suits you better, How to measure a Pomodoro day without a Pomodoro app runs the same kind of comparison on shorter intervals.

Questions

Do I need a timer for the block itself?

A timer or an alarm in the Clock app is useful to mark the end, so you are not checking the clock. The record of the day does not need it; that runs on its own.

What if a meeting lands on my block?

Move the block, not the test. Note it in your one-line log so you know why that day looks different.

Does a Focus mode affect the record?

A Focus holds back notifications. It does not change which app is in front, so the record still shows exactly where your time went, including any app you opened anyway.

How long should I run the test?

Two weeks is the minimum to compare one week against another. If the result is close, run a third week to see which way it settles.