This is another of those things I have struggled with in the English language. In Norway, Sweden, and I guess also Finland we say good morning maybe until 9 am. After that it is sort of a little rude to say good morning. Sometimes you might get a comment back if you say it, someone will say, "do you think I just got up", if you say it after 9 am. Like you are indicating they overslept or even worse, was lazy. After 9 it is good day, and it continues with good day maybe until 3pm. Then it becomes afternoon, for until like 6 or 7 pm, then it becomes evening, not night. And it is then evening until you go to bed, like 10-11 pm, then it is good night and you go get your tush under the comforter. And then it is night until the rooster announce the new morning.
Very different from here in the US.
Noon in Norwegian is "middag", which means "mid-day", in other words, if the day starts at 9 am, and last until 3 pm, 12 will be in the middle of that day. "Middag" also means dinner, because that was when people in the old days in Norway ate the only warm meal they had in a day.
Bill