Switching to 24-hour clock solves that problem.

Personally, 12h clock always confused me, so I wouldn't blame Siri.

Siri still uses AM/PM for me when speaking, despite having a 24-hour clock configured.

Its given that a dentist appointment is never usually at 10PM - this doesn't seem probable. LLMs are good at generalizing

And also, that would still be more useful than the current situation where Siri would just answer that it can not give you the weather forecast because there is no city named "Appointment at 10".

Or it may create an appointment at Athens.

Siri without it isn't though. It's so garbage as to be useless.