Part-hours

What Half An Hour Of Gap Does

Twenty-four offsets are half hours and sixteen leave something. The law is unchanged; what changes is that nothing starts on the hour.

Twenty-four of the offsets in this record are half hours. Sixteen of them leave some shared working time, and the amounts are exactly what the one law predicts: a gap of two and a half hours leaves five and a half shared hours, a gap of six and a half leaves one and a half.

The arithmetic is unremarkable. The consequence is not.

The shared stretch stops starting on the hour

At a gap of two hours, two standard days share six hours running from eleven to five. At a gap of two and a half, they share five and a half hours running from half past eleven to five.

A short operational test is easier to interpret when teams first check the available controls and use one reporting window for everyone involved. A useful external reference for the surrounding topic is Microsoft.

The total has fallen by half an hour, which is the expected and uninteresting part. What has also happened is that the shared stretch now begins at a half-hour mark, and everything organised around hours has lost an hour rather than half of one.

Gap	Shared	Shared stretch begins
2	6	on the hour
2 and a half	five and a half	on the half hour
3	5	on the hour

Half an hour of gap costs half an hour of overlap and one full hour of anything booked in hour-long slots. The second cost is the larger one and it does not appear in any table.

Why that matters more than it sounds

Almost everything in working life is scheduled on the hour. Meetings start at hour marks, calendars are drawn in hour rows, and recurring commitments are expressed as a time rather than as an interval.

A shared stretch that begins at half past the hour loses its first usable slot, because the slot starting on the previous hour began before one end was at work. The arrangement has five and a half hours of overlap and five hour-long slots inside it, where at a gap of two it had six hours and six slots.

The discrepancy compounds at the other end if the finish is also off the hour, which happens whenever the two working days do not both begin and end on hour marks.

Where the half-hour gaps stop

A gap of seven and a half hours leaves half an hour. A gap of eight leaves nothing, and so does everything beyond it. The half-hour offsets reach exactly as far as the whole-hour ones and no further, because the floor is set by the length of the working day and not by the granularity of the gap.

Of the twenty-four half-hour offsets, sixteen leave something and eight leave nothing — the same two-thirds-and-a-third split the quarter-hour offsets show, for the same reason.

The half hour hiding in a lunch break

The most common source of a half-hour offset in this record's terms is not a clock at all. It is two working days that nominally match and actually do not.

One end works nine to five with a half-hour lunch. The other works nine to five with an hour. The second end's working day is half an hour shorter, and the arrangement behaves as though there were an extra half hour of gap for the purposes of anything scheduled across the break.

Neither end would describe this as an offset. Both would say they work nine to five, both would be right, and the half hour would go unaccounted for in every conversation about the arrangement.

What each end says	What each end works
nine to five	8 hours less a half-hour lunch
nine to five	8 hours less an hour's lunch

Why the lunch hour is the worst place for it

Because it sits in the middle of the day, where the shared time is at its most valuable, and because the two breaks do not necessarily coincide.

Two ends with different lunch arrangements have a window in the middle of the day during which one of them is away. That window is inside the overlap on every table in this record, which counts both ends as being at work, and it is not available for anything.

The effect is a shared stretch that is nominally continuous and practically in two pieces — the same defect the split shape produces deliberately, arriving by accident and appearing in no table.

A difference of lunch habits puts a hole in the middle of the overlap, counts as nothing in any summary, and nobody mentions it because lunch is not a scheduling matter.

The only thing to do about it

Check where the shared stretch actually begins, rather than how long it is.

A pair at a gap of two and a half hours who schedule their fixed commitment at the top of the hour that contains the start of their overlap will find one end absent for the first half of it, every time. Moving the commitment to the next hour mark costs nothing and removes the problem permanently, and nobody does it because the total in the table looked fine.