What an all-day event really means
An all-day event is not twenty-four hours long. It is not any number of hours long, which is exactly why it behaves oddly when you expect it to.
What most people assume
That an all-day event is an event that runs from midnight to midnight.
It belongs to a date, not a clock
A birthday is on the fourteenth everywhere on earth at once. It does not start earlier in Tokyo. All-day events model that: they are attached to a date and carry no time zone at all.
This is why they do not shift when you travel, while everything else does.
Where people fight it
Using all-day for a conference that really runs nine to five means it cannot collide with anything, so the calendar stops warning you about clashes on that day.
If you want the day blocked, block the hours. If you want the day labelled, all-day is correct.
What it looks like
What to do
- Use all-day for dates: holidays, birthdays, deadlines, travel days.
- Use timed events for anything that can collide with something else.
- For multi-day trips, an all-day span plus timed events inside it reads best.