Write down the actual constraints
Start with the cities, a real date, and the availability each participant can offer. A default 09:00–17:00 day is a useful demonstration, but it cannot tell you about someone’s shift, school pickup, lunch break, or willingness to join early. Ask for the constraints that matter before interpreting a highlighted window as a recommendation.
Use one three-way intersection
On 27 October 2026, suppose New York, London, and Berlin each offer 09:00–17:00 local time. Their common interval is 13:00–16:00 UTC: 09:00–12:00 New York, 13:00–16:00 London, and 14:00–17:00 Berlin. New York sets the opening boundary and Berlin sets the closing boundary.
Checking pairs separately can mislead you. A city may overlap one colleague in the morning and another in the afternoon while all three have no time in common. Keep every participant in the same plan so that the result refers to one shared instant.
Fit the end as carefully as the start
A 90-minute meeting can fit inside that three-hour interval. Its latest start is 14:30 UTC, which finishes at 17:00 Berlin. Starting at 15:00 UTC would still be inside everyone’s day at the beginning, but the final thirty minutes would overrun Berlin’s limit.
Now shorten London’s offered day to 09:00–14:00. The shared interval becomes 13:00–14:00 UTC, only one hour. The tool should show the shortfall. Changing a ninety-minute discussion into a sixty-minute one may help; merely clicking a green start time does not.
Decide what fairness means for this group
The earliest acceptable time may consistently burden one person. The mathematically widest interval may still be poor for a participant who has offered an exceptional evening. Discuss whether to rotate an inconvenience, split the discussion, reduce attendance for one section, or use an asynchronous update.
The availability controls record an agreement; they do not create one. When widening someone’s hours, confirm that change with them. Keep the normal hours visible in your own planning notes so an occasional exception does not silently become the assumed routine.
Check again when the date changes
With the original 09:00–17:00 hours, the common window becomes 14:00–16:00 UTC after New York’s November 2026 change. A weekly plan therefore needs the twelve-date preview. Review both the start and the duration on each row before taking the agreed schedule into a calendar.
Sources
Follow the original references for the rules and formats used in this guide.