How the problem develops
An invitation says 10:00 without a zone, or a copied confirmation uses yesterday’s offset. Participants agree on a clock time but not the same moment. Daylight-saving changes make fixed offsets particularly easy to misuse.
What to check first
- Compare the booking page, stored event, invitation and reminder for the same appointment.
- Check whether the system stores a named time zone or only a manually typed offset.
A better process
- Use a named time zone and preserve the confirmed appointment instant.
- Display the zone alongside human-readable times in confirmations.
- Test date boundaries and seasonal changes, including rescheduling across them.
What a system can do
Convert the confirmed event into the attendee’s selected display zone and generate reminders from that event.
Where people stay in control
Do not infer a preferred time zone solely from an email domain or nationality. Let the attendee confirm it.
Benefits and tradeoffs
The useful outcome
Everyone can verify the same appointment without doing a separate conversion.
The tradeoff
Calendar tools and old invitations can disagree after settings change. A correction process is still needed.
Test before going live
Test Bangkok with London and New York dates around seasonal clock changes. Compare actual calendar events, not just the confirmation text.