Honestly I prefer saying "Good Day" in Czech as well (that's the most abundant one used here).
At some point I realized that the whole thing has silent "I wish you", which also means that if I say "Dobrý den" (=="Good day") I'm actually being more generous. So correcting me to "Dobrý večer" (== "Good evening") because it's 7 PM or whatever is actually not just petty but also kind of a dick move.
(Edit: I also realize that my explanation is probably the pinnacle of pettiness, with just a little pinch of dickmoveines on top...)
You are correct. Good night means that whatever you've been doing is over. The media is bending over backwards trying to appear "fair", but it just results in moments like this.
I've found that the answer depends on what region of the US you're from. The UK probably does it differently, but I'm with @FlyingSquid@lemmy.world. If it's dark out, you're definitely greeting with "good evening."
what would you say in a greeting like that if it was, say, 1:00 AM?
I'd probably say: "Why are you still up? Your bedtime was hours ago. GO TO BED!" because it would most likely be one of my children at that time of night.
In USMC boot camp, this specific topic was addressed very early on. It's "Good Morning" up until noon, after which it is "Good Afternoon" up until you eat evening chow, then it is "Good Evening" until midnight (at which point it becomes "Good Morning" again).
Of course, it's all up to personal preference in the real world. If you're out with your friends at a club and it's after midnight but still very much dark out, you're not going to be greeting people of the gender that you prefer to look at with "Good Morning", because it is still 'evening' to you and them.