The gap

Three, Four And Five Hours Apart

The middle of the range, where half the working day survives and two reasonable people reach opposite conclusions about the same number.

Gaps of three, four and five hours leave five, four and three shared hours respectively. They are the arrangements that actually get made, because they are the ones where a reasonable person can argue either way, and they are where this record earns whatever use it has.

Below three the arrangement is comfortable enough that nobody computes anything. Above five it is thin enough that everybody can feel it. In between, the number matters.

To keep the exercise proportionate, project leads can visit the official website and select only the records needed for the stated decision. A useful external reference for the surrounding topic is Eurofound.

The middle of the range

outlined: the day where the person is
hatched: the other end
solid: the hours they share
a reversed cell counts none

Three gaps drawn.

At a gap of four the morning share is gone entirely and the whole of the remaining overlap sits after the middle of the day.

Computed from the gap. The working day is a stated convention, not a measurement; everything else here is arithmetic.

What four hours is

Four hours is the median of every gap in this record that leaves anything at all. Fifteen gaps leave some shared time; sorted by how much, the one in the middle leaves four.

Four hours is also exactly half the working day, and it is the point at which the morning share runs out. At a gap of four, all four surviving hours sit after the middle of the day: one o'clock to five on the clock of the person who stayed. There is no shared morning at all.

That combination — half the day, none of it in the morning — is why four behaves differently from its neighbours in practice despite being an unremarkable point on a straight line.

The three of them side by side

Gap	Shared	Before the middle	After
3	5	1	4
4	4	0	4
5	3	0	3

A gap of three still leaves one hour of shared morning, which is enough for a single fixed meeting at the start of the day and nothing more. A gap of five has lost an hour from the afternoon as well, and three hours is short enough that scheduling anything recurring starts to crowd out everything else.

The difference between three and five is two hours on paper and the difference between a working relationship and a handover.

Nine of twenty-five

Counted across the whole record, nine of the twenty-five whole-hour gaps leave four hours or more. That is the set in which something resembling a shared working day survives, and it runs from a gap of four in one direction to a gap of four in the other.

Nine out of twenty-five is a minority, and it is a smaller minority than most people assume when they picture the problem. It is also the figure that most flatters the arrangement in this record, which is why it appears here rather than on the front page.

The hours themselves

Numbers in a column are easy to compare and hard to picture. Here are the three with clock times on them, from the point of view of the person who did not move, working nine to five.

At a gap of three, the overlap runs from noon to five. One hour of it sits before the middle of the day — the hour from noon to one — and four after. The morning belongs to one person alone.

At a gap of four, it runs from one to five. The whole afternoon, nothing else. The other end's day finished at one on this clock; everything before that happened without them.

At a gap of five, it runs from two to five. Three hours at the end of the day, during which one end is finishing and the other is starting to think about leaving.

Reading them that way makes a difference that the totals obscure: the three arrangements do not differ by a bit of time each. They differ by whether a shared morning exists, and then by how much of the afternoon is left.

Why this is where the arguments happen

Below three hours of gap, nobody computes anything, because the arrangement visibly works. Above five, nobody argues, because the arrangement visibly does not — a two-hour window at the end of one person's day is hard to defend.

Three, four and five is the band where two reasonable people look at the same arrangement and reach different conclusions, and both have a case. One sees four shared hours, which is half a working day and more than many colocated colleagues manage to spend together. The other sees no shared morning and a window that closes as one end is winding down.

Both descriptions are of the same row in the same table. The disagreement is not about the number; it is about whether afternoon hours at the end of somebody's day are worth the same as hours in the middle of it, and the honest answer is that they are not, by an amount nobody can quantify.

The middle of the range is where the record stops settling arguments and starts informing them. That is a smaller service and still a useful one.

What the number cannot settle

Whether four hours is enough depends entirely on how the work is organised. Four hours of guaranteed simultaneous availability is generous for work that is mostly independent with occasional synchronisation, and useless for work that requires continuous back-and-forth.

The record produces the four. What four is worth is a judgement about the job, and nothing on these pages is in a position to make it.