Same instant
One moment, two civil times
12:00 in London is not noon everywhere. It is a named instant. New York's clock for that instant is what this page prints.
Choose two cities and a local time. The result is the same instant, not a second independent clock.
Daylight saving
London and New York are five hours apart for most of the year and four hours apart for a few weeks in March and October, when only one of them has changed clocks. The converter uses IANA dates, not a fixed offset.
Same instant
12:00 in London is not noon everywhere. It is a named instant. New York's clock for that instant is what this page prints.
Overlap
The meeting planner marks hours that fall inside 09:00-17:00 in every city you pick.