My computer is configured correctly, but it's rather common for an application (especially a phone app) or website to ignore those settings, or to think it knows better.
04:30 UTC means 04:30 UTC, or 05:30 in Denmark. Not 17:30!
The same can happen if I type something like "04:30 Catch flight" into an appointment in my Google Calendar. It is converted into a new appointment "16:30 Catch flight".
It's not just Google. "Your Office 365 subscription will automatically renew on 1/19/2018." and the admin interface is a mix of date and time formats.
Uh, yeah, I'm well aware of that, as are most Americans I know. That's why I asked about "the American assumption that everyone uses the 12-hour clock". That must be a myth that non-Americans believe in.
It's definitely in keeping with how we mix meters/feet and pints/litres.
I'm an American, and I was not aware of the "American assumption that everyone uses the 12-hour clock." Please elaborate further.