Write both endpoints as complete instants
A note saying 22:00–01:00 leaves out the date of its ending clock label. For an overnight window, write the start date and next-day end date explicitly. Preserve each supplied offset. A UK-local display should not replace the original source instant or silently choose a different time zone.
This case concerns time you have entered for research, not an exchange calendar. It does not establish when a venue trades, whether a holiday applies or whether an instrument is available. The same arithmetic can compare two personal reading windows when their underlying instants are known.
Compare the later start with the earlier end
In an invented example, window A runs from 21 October 22:00+00:00 to 22 October 01:00+00:00. Window B runs from 22 October 00:30+00:00 to 02:00+00:00. The later start is 00:30 and the earlier end is 01:00 on the same second date: the overlap is 30 minutes.
Writing 01:00 on the first date instead would reverse A’s chronology. Do not repair a negative duration by automatically adding a day unless the original instruction explicitly defines an overnight convention. An invalid interval and an empty intersection are different states.
| Fictional item | Full date or interval | Result |
|---|---|---|
| A | 21 Oct 22:00 → 22 Oct 01:00, +00:00 | 3 hours |
| B | 22 Oct 00:30 → 02:00, +00:00 | 90 minutes |
| Common portion | 22 Oct 00:30 → 01:00, +00:00 | 30 minutes |
Declare whether a touching endpoint counts
For a duration calculation, use the explicit half-open convention [start, end). If B instead begins exactly when A ends, the common duration is zero. You may describe that as a boundary touch, but it is not a usable half-hour work period.
If your task assigns discrete events to windows, its inclusion rule needs a separate definition. Do not count one event twice merely because one window ends at the instant the next begins. Save the convention with the result so another person can reproduce the classification.
Use instants when two sources display different offsets
Two notes both labelled 00:30 can refer to different instants if one has +00:00 and the other +01:00. Convert their complete timestamp representations to one comparison basis before taking the later start. Keep that conversion alongside the original values so a reader can identify an offset error. An equal clock display is not an automatic overlap, and a calendar-date change alone does not tell you whether the two actual intervals intersect.
Retain the inputs when displaying a UK summary
A useful sheet keeps the four original endpoints, any converted display values, the chosen convention and the resulting duration. Unknown offsets remain unresolved. Equal clock labels from different sources do not prove equal instants, and a date-only value cannot support a minute-level overlap claim.
This companion case adds an intersection and endpoint audit to a time-conversion workflow. It does not choose a trading session or recommend acting during the overlap. Every date and interval in the example is a teaching input rather than a current market schedule.
The optional link below leads to this site's separate crypto signals and Telegram updates offer. The record method is usable without that offer. It does not independently verify the offer, establish country eligibility or turn the teaching example into an actual transaction.
Primary sources and scope
- RFC 3339: Internet timestamps
Full dates and explicit numeric offsets; a timestamp representation does not prove clock synchronisation. Checked 2026-10-21.