@GrahamDowns I think that's the thing with English, a lot of words are vague.
In the Tagalog and Filipino languages, as well as Filipino culture, we don't have this confusion that English has.
If one is referring to the clock, we just use “a.m.” or “p.m.”. Or, if one wants to use daylight, or the lack of it, we just say, “gabi pa“ or “madilim pa” (which would be, in this context, “it's still dark” --- “gabi pa” if translated without context is “it's still night”).
In Korea, if I am not mistaken, they use words “night” (not p.m.) once it is 19:00 onwards, even though it's still very bright. They use a 24-hour clock system but they don't really use it in regular conversation.
For someone like me from the Philippines, it's confusing at first, because “day“ and “night” is understood as the presence of sunlight, or lack of it. If we're referring to the clock we use, as mentioned, “a.m.” or “p.m.”.
Although, recently (or a few years ago?) you will also hear “four ng umaga” (four in the morning) instead of “4 a.m.”.
In the 80s, my grandparents start to use “gabi” (“night”) once the clock strikes 18:00, regardless if it is still bright or not.
I guess it depends on your generation and how you adapt to the changing culture and how we use words?
PS
The Philippines doesn't use the 24-hour clock system. Not even unofficially. I'm one of those few non-military citizen who prefers it, because it is easier and clear.
So, if I say, Tuesday at 00:00, it means the 12:00 midnight between Monday and Tuesday.
And if I say Tuesday at 24:00, it means the 12:00 midnight between Tuesday and Wednesday.
So far, at least as far 24:00 vs 00:00 are concerned, most Filipinos I talked to where this midnight mattered, they understood the difference between “Tuesday, 24:00” and “Tuesday, 00:00”.
Oh, I just remembered, in Korea, Thailand, and I think also in Vietnam and Laos, they use 25:00, 26:00, and 27:00. However, they only use it for TV and radio programming.
I'm not sure if you have something similar there. But I think it has to do with psychology.
If they say that the show will air at “Tuesday, 2:00 a.m.” or “Tuesday, 2:00 in the morning”, people tend to sleep and will be lazy to wake up.
However, if they say, “Monday at 26:00”, people are conditioned not to sleep because they are thinking “it is tonight, not tomorrow morning”.
And that “it is tonight, not tomorrow morning” is a contradiction to how they tell time conversationally.
Took me a while to understand why they were doing that. (I learned it back in the 90s, when cable TVs were a thing.)