Daylight is a constraint, and calendars usually ignore it
Weather is uncertain. Daylight is not, and yet most plans are made as though only the first one existed.
What most people assume
That the light will hold because it held last week.
The number moves faster than intuition
Around the equinoxes sunset shifts by two to three minutes a day at mid-latitudes. Over a fortnight that is half an hour, which is the difference between finishing in light and finishing by phone torch.
In late autumn the change is sharpest exactly when people are still scheduling as though it were September.
Use it as a hard edge
Unlike rain, sunset is certain. It is the one planning input that never surprises you, and it deserves to be treated as a wall rather than a suggestion.
Work backwards from it: a two-hour activity that must finish in daylight has a latest start, and that start moves every week.
What it looks like
What to do
- Work backwards from sunset for anything outdoors, not forwards from the free slot.
- Re-check the latest safe start every couple of weeks in spring and autumn.
- In the fortnight after the clocks change, assume your instincts are an hour wrong.