You aren't reading what I wrote. None of this matters if it only affects a single person/organization. It doesn't matter what time zone you are in, it will "ju

You aren't reading what I wrote. None of this matters if it only affects a single person/organization. It doesn't matter what time zone you are in, it will "just work," the only thing that is different is the amount of effort required by the dev. Even then, there's probably going to be a delay while tzdata is updated downstream and on the servers/phones/etc. It only matters when you have people in multiple timezones. A better analogy would be if you set an alarm to go off 7AM London time, for me, and I am in Amsterdam time. When the UK decides to switch to UTC+5, that 8 AM alarm (CEST) won't go off ... instead it will go off at 13:00 CEST. That is why you need to notify users that have an appointment in a different, affected, timezone.