How to call what part of the day & why?

Question

In the old days sunrise to sundown = Day, sundown to sunrise = Night.
Since people are keeping time, a day is 24 hours, running from midnite to midday, with phrases like morning, afternoon, evening & night. Where does one part start and ends??
I had a discussion about this with my gf, who stated that from midnite to midday it is morning, while i say midnite to sunrise is nite, sunrise to midday is morning. Most people do agree that midday is where morning goes to afternoon.
I do tend to call it morning untill i have my lunch, using that as switch between morning & afternoon.

So how do you see that? do you spllit a day in 4x 6 hrs? or just how you feel?
Tx

Answer 1

I say tonight but i also would say this evening for same times afternoon i'd say finishes about 7 .
so this evening at 7 im watching tv but can say tonight at 7 im watching tv.
weird lol
If its after 12 midnight say its tueday i'd say to people see you tomorrow even though i'm talking about tuesday .
but then i'm weird.