I just found that someone posted something at 12:01 AM and I had no idea whether that was one minute after midnight (00:01) or one minute after noon (12:01). So I looked it up.
12-hour clock is used in USA and UK alike. The AM stands for ante meridiem (before midday) and the PM stands for post meridiem. There is no zero hour in 12-hour clock.
- 12:00 AM – midnight, the new day starts
- 12:01 AM – one minute after midnight
- 1:00 AM – one hour after midnight etc.
- 11:59 AM – last minute before the noon
- 12:00 PM – noon (12:00 in 24-hour cycle, too)
- 1:00 PM – one hour after noon
- 11:59 PM – one minute before midnight
In the Czech Republic, we usually use the 24-hour time notation, at least in writing. Of course, we say “we’ll meet at six” and we don’t mean at six in the morning. But we would never put it like that in an official document, 18:00 is the way to be unambiguous (jednoznačný).
It is funny that Americans call our time notation “the military time”, except the colon (dvojtečka) is omitted. You might remember it from Phoebe’s Wedding in Friends, where Monica is using military time to give the impression of fierce, precise organizer. In Czech notation, we usually say “twenty-three zero zero”, whereas military time reads: “twenty-three hundred”.