Converting a time
Choose a source city, set a date and time, and every other city on your list shows the matching local time. The date matters: the offset between two cities is not constant through the year, because daylight saving starts and ends on different dates in different countries and some places do not observe it at all. Converting a meeting in November using an offset you looked up in July is one of the most common ways to be an hour late.
The overlap strip
Below the conversions, each city gets a 24-hour strip shaded by how reasonable that hour is locally: green for a 9-to-6 working day, grey for awake but outside working hours, and empty for the middle of the night. Reading down a column shows you instantly which hours work for everyone. For a call spanning San Francisco, London and Singapore there is usually exactly one, and it is not a comfortable one for at least one of them.
Crossing the date line
When a converted time lands on a different calendar day it is labelled as the next or previous day rather than left for you to work out. This is where most scheduling errors happen — a 4 p.m. Thursday call in New York is 6 a.m. Friday in Sydney, and dropping the day is how people miss meetings entirely.
Sharing the comparison
Copy share link encodes the source city, the target cities, and the date and time into a URL. Send it and the other person sees exactly what you see, with no account and nothing to install. It is a faster way to settle a scheduling thread than another round of "does that work for you?".