A 10am PDT America/Los_Angeles meeting is different from a 6pm BST Europe/London meeting which is different from a 5pm GMT meeting and those will jump around by an hour depending on time changes. If the bulk of your team is in Seattle then you probably want to pick the US timezone for the meeting and not GMT or London. If you have a manager in London, though, who sets up the meeting time in their local timezone then Seattle employees will notice tomorrow that the meeting is a hour later in Seattle than it normally is.

If everyone shitcanned clocks jumping around twice a year this craziness would end.