Worked example · Autumn 2026
One team, three cities, three different autumn offsets
A standing meeting between Tokyo, London, and New York needs another look when clocks change. The cities do not all change their offsets together.
The two clock changes
GOV.UK lists October 25 as the UK's 2026 return to Greenwich Mean Time. NIST lists November 1 as the end of US daylight saving time in 2026. That leaves several days when London has changed clocks but New York has not. Tokyo stays at UTC+09:00 in these examples.
The London–New York difference is five hours on October 20, four hours on October 28, and five hours again on November 3. A conversion remembered as “London is five hours ahead” misses the middle case.
What 17:00 in Tokyo becomes
| Date in 2026 | Tokyo | London | New York |
|---|---|---|---|
| October 20 | 17:00 · UTC+09:00 | 09:00 · UTC+01:00 | 04:00 · UTC−04:00 |
| October 28 | 17:00 · UTC+09:00 | 08:00 · UTC+00:00 | 04:00 · UTC−04:00 |
| November 3 | 17:00 · UTC+09:00 | 08:00 · UTC+00:00 | 03:00 · UTC−05:00 |
These are conversions of one instant, not recommended meeting times. Starting at 17:00 is already outside a Tokyo window that ends at 17:00 when the meeting has any positive duration. It is also extremely early in New York.
Why a standard workday has no three-way overlap
With 09:00–17:00 working hours in all three cities, no meeting of the supported durations fits everyone on these dates. On October 20, Tokyo's window is 00:00–08:00 UTC, London's is 08:00–16:00 UTC, and New York's is 13:00–21:00 UTC. Tokyo and London touch at a boundary, leaving no room for a full meeting; New York starts much later.
After London's change, its window starts at 09:00 UTC, making even that boundary disappear. After New York's change, its window starts at 14:00 UTC. Changing the reference city changes which date you are exploring; it does not create working-hour overlap.
A transparent exception is better than a hidden one
If everybody agrees to a 30-minute call at 21:00 Tokyo time, London sees 13:00 on October 20 and 12:00 on October 28 and November 3. New York sees 08:00 on October 20 and October 28, then 07:00 on November 3. The burden shifts even though Tokyo's start stays fixed.
Ask before making those exceptions. For example: “The November 3 option is 21:00 in Tokyo and 07:00 in New York. Can both teams accept that for 30 minutes?” If the answer is no, split the discussion or use an asynchronous handoff.
To reproduce the comparison, choose Tokyo as the reference city, add London and New York, enter each date separately, and keep the real working windows. Review every local date and offset before exporting an event. Read the planning guide for duration checks, sharing, and calendar imports.