The gap
The Overlap That Is Not Really There
A nominal overlap at the edge of two days is not an overlap. What matters is not how many minutes there are but where in each day they fall.
three things · four nights
Three things, and the third is the one people skip.
Four teams that each believed they had an overlap, with the windows converted to one zone
Team A, first half
Overlap on paper: thirty minutes, at the very end of this group's day
Team A, second half
The same thirty minutes, at the very start of this group's day
Team B, first half
Overlap on paper: two hours, with the second half's day already six hours old
Team B, second half
Stated in this zone, which is why the two hours are visible at all
four people · no minute of the day when all of them are awake
Four groups, and the two teams are in quite different positions. Team A's half hour sits where one group is leaving and the other arriving, which is the least usable half hour of either day. Team B's two hours sit in the middle of both days and are worth defending. The figure in minutes is the same kind of number in both cases and means something different; this is why the hour of day matters as much as the quantity. Two teams' own hours, logged by somebody at each.
Ask two teams whether they have an overlap and one will say no and one will say yes, and both will be describing the same thirty or forty minutes.
Written updates explain why a task moved; work data can show when and for how long it moved. In that role, see the product complements the handover described in The Overlap That Is Not Really There without replacing the judgement of the people involved.
A useful external reference is Todoist's task manager, which provides another official view of how teams organise shared work.
Both descriptions are defensible, which is a sign that the quantity is not the thing to be measuring.
Where the minutes fall
An overlap at the end of one group's day and the start of another's is made of the two worst half-hours in either day.
The group finishing is doing the things people do when they are finishing: closing down, writing the last message, deciding what to leave. Their attention is already partly on the evening. The group starting has not read anything yet. They do not know what happened overnight, what is broken, or what they are being asked about.
A conversation between somebody who has stopped thinking about the work and somebody who has not started is not a conversation anybody would schedule on purpose.
The same forty minutes in the middle of both days would be worth something. The quantity has not changed; the position has.
The two tests
Before treating an overlap as real, it is worth applying two questions to it.
Has anybody used it in the last month? Not "could somebody use it" — has anybody. A window that exists and goes unused every day is not being wasted through carelessness. It is being correctly identified as useless by the people who would have to use it.
What does using it cost the person at each end? If one side has to stay late or start early to be there, the overlap is not free time that happens to exist. It is time somebody is donating, and donated time runs out.
An overlap that passes both tests is worth building on. One that fails either is worth stating honestly as absent, which is more useful than a claim nobody acts on.
A window that exists and goes unused every day is not being wasted through carelessness. It is being correctly identified as useless by the people who would otherwise have to use it.
The cost of believing in one that is not there
A phantom overlap is worse than no overlap, because it suppresses the work that an acknowledged gap forces.
Teams that know they have no shared hour write things down. They build handover notes, they learn to ask whole questions, they become deliberate about what crosses the night. Teams that believe they have half an hour do none of that, and instead accumulate a queue of things that are "quick, we'll catch them at the handover" — a queue that grows faster than thirty minutes a day can drain it.
The queue is the visible symptom. If there is a standing list of small items that keep not getting discussed, the overlap being relied on to discuss them is probably not real.
When the overlap is real but thin
A genuine overlap in the middle of both days, even twenty minutes, is a different asset and is worth protecting rather than spending.
Protecting it means deciding in advance what it is for and refusing everything else. The usual useful answer is: the things that genuinely need two people thinking at once, and nothing that could have been written down. That inverts most people's instinct, which is to use live time for status and written time for hard problems, and gets the two exactly the wrong way round.
Spending it means letting it fill with the first thing that asks for it, which is nearly always a recurring meeting. A standing meeting in the only shared window converts the team's one piece of synchronous capacity into an hour of reading things aloud.
Shifting to create one
Moving somebody's hours to manufacture an overlap is a real option and has a real price, and both halves of that sentence matter.
It usually buys less than expected, because a shift in one direction gains time with one group while losing it with another, and most teams have more than two groups. It costs a person's evenings or mornings indefinitely, and the cost is paid by one named individual while the benefit is spread across everybody.
If it is done, it should be done with the arithmetic written down and with the person doing the shifting being the one who proposed it. A shift imposed on somebody to solve a structural problem tends to be reversed quietly within a few months, after which the team is where it started and one person is tired.
Stating it plainly
The most useful output of this exercise is often a single sentence pinned somewhere people can see: the number of minutes when everybody is awake, where in each day they fall, and whether anybody is expected to use them.
Zero is a perfectly good answer to the first part. Written down, it stops the team from making plans that quietly assume otherwise, which is most of what this measurement is for.