Two opposite ideas about how work gets done: one asks for whole uninterrupted hours, the other for short repeated stretches. It is worth looking at where they disagree, because on one thing they very much do not.
Cal Newport, in a 2016 book, argues that valuable work asks for long protected blocks, and that jumping between tasks leaves a trail behind: part of your attention stays stuck on the previous thing. His conclusion is blunt: fewer switches, longer blocks, and a boundary that other people respect too.
The price of this position: a long block has to be defended, and not every day allows it. Someone with small children, on-call work or a noisy house is not choosing to be fragmented.
On the other side sits the tradition of 25 minute timers: a short stretch, a break, and again. The advantage is that a short stretch can be started even on a broken day, and that the end is close enough to stay believable while you look at it.
The price: some work does not fit into twenty-five minutes. Reopening something complex costs, and paying that cost four times is not free.
The two schools argue about duration. But if you look at what they ask you to do, they ask for exactly the same thing: a boundary. A stretch of time that starts and ends, decided in advance, and not left to however the day goes.
Neither of them says "work until you run out". Both say: decide now how long it lasts, then keep to what you decided. That is where the difference between a full day and a long day sits, not in the number of minutes.
We do not choose for you here: slots are 25 and 50 minutes, and you can put two back to back. This is the rule of thumb we would use.
If you finish early you can close early: the slot is a boundary, not a box to fill. And if you want to try the short shape without an account, there is a 25 minute timer that runs in the browser.
Yes, with no penalty: each slot is chosen on its own when you book it.
Yes. They are two appointments next to each other, so between them there is a moment where you can stop without leaving anything half done.
You can close whenever you want. The slot is there to put a boundary down, not to fill every minute.
The ideas are summarised, not quoted, and credited to the people who wrote them. No text is taken from the books.