> - US (and maybe one or two English-speaking countries) are the only ones using 12h time, the rest of the world uses 24hrs, however 12h _sometimes_ is used conversationally;

For German speaking countries: rather always#. In fact, you don't even say 3 PM. Just "drei". I think everything from 8 AM to 7 PM is considered "business hours" - and everything else needs clarification ("4 in the morning").

And we call 0:00 "12 Uhr Mitternacht" as well, I think nobody says "0 Uhr". But at least writing it down makes sense.

# Nobody I knows really uses "15 Uhr" to say 3 PM (people might sometimes do, but I never hear it, it sounds wrong, maybe "nerdy")