How long a block should be, and the 60 percent rule

Two sizes cause most of the failures: the block that is too short to be a block, and the day that is too full to be a day. The second is why people quit in week two.

The UnaTask team, Building UnaTask. Aug 21, 2026. 5 min read.

The first schedule anybody builds is beautiful and wrong in the same two ways. The blocks are thirty minutes because that felt reasonable, and there are enough of them to fill the day because leaving gaps felt like slacking. Both instincts are backwards.

The four lengths, honestly

25 to 30 minutes. One small defined thing, or a batch of near identical fragments. Not a block for thinking work. Observed office workers already get stretches around eleven minutes for free, so half an hour sits barely above the ambient fragmentation of a normal day and buys you almost nothing structural.
50 minutes. The workhorse. Long enough to get in, short enough to fit between commitments, and it leaves ten minutes on the hour for closing properly.
80 to 90 minutes. Real depth. This is where work that has to be held in your head all at once actually happens. One or two of these in a day is a strong day, not a modest one.
Half a day. Only for work with a genuine warm up cost: a hard debugging session, a first draft, a design pass. Rare, and worth defending out loud when you schedule one.

The 60 percent rule

Do not block more than about 60 percent of your working hours. On a seven hour day that is a little over four hours of blocked work, and when you first write it down it will feel like giving up before you have started.

It is not. The remaining 40 percent is where the day's actual events live: the thing that broke, the question that could not wait, the meeting that ran over, and the twenty minutes you spent recovering from all three. A day blocked at 100 percent is not an ambitious plan. It is a plan that is guaranteed to be wrong by eleven in the morning, and a plan that is always wrong stops being consulted.

Blocking less is not lowering the bar. It is the difference between a plan you keep using and one you stop opening.

The failure this prevents, specifically

Nearly everyone who abandons time blocking abandons it in week two, and almost always for the same reason. They blocked every hour. Reality took four of them. By Thursday the calendar had become a daily record of falling short, and nobody keeps opening a document that exists to tell them they failed.

The unblocked 40 percent is also where your estimation error gets absorbed instead of cascading. Every block that runs over pushes the one after it, so a thirty percent underestimate on the first task of the day becomes an entirely fictional afternoon. Gaps are not politeness. They are the shock absorber.

What a realistic day looks like

A deep block of ninety minutes in the morning on the one thing that matters. A quarter hour after it to land, before anything else starts. The meetings you did not choose. A second pass of eighty minutes on the same piece of work in the afternoon, because a second pass on the same thing starts warm while a different thing starts cold. One fifty minute batch for everything small, at the hour when careful thinking is expensive and sorting is cheap. Then an hour and a bit left deliberately unclaimed, and ten minutes at the end to plan tomorrow.

Count it and that is three hours and fifty minutes of work you chose, in a working day of seven and a half hours. Fifty two percent. It looks thin on paper and it is more than most weeks deliver.

The guide has the whole day drawn out, plus a printable weekly template. Free PDF, no email, and every number in it traced to the paper it came from. Get the full guide