Calendar & Timeline — Which clock the calendar runs on

Record dates are stored as plain wall-clock time, and the workspace time zone (Settings) says which wall that clock is on. A shift at 9:00 AM is 9:00 AM at the site, whoever is reading the rota — which is the behaviour you want almost always, and it is the default. For the times that genuinely belong to the people in them rather than to a place — a call, a remote session, a cross-border booking — turn on Show in each viewer's time zone on the date field. Then 3:00 PM London shows as 10:00 AM to a colleague in New York, and dragging it works in their terms too. Nothing changes for anyone who has never set a time zone on their own profile: they see the workspace's times exactly as stored.