Student or Learner
What time should we change the greeting from good morning to good afternoon?
What time should we change the greeting from good afternoon to good evening?
Can we also say "good noon"?
12:01am to 11:59am -- good morning
12noon to 4:59pm -- good afternoon
5:00pm to 7:59pm -- good evening
8:00pm to 12midnight -- "hi" or "hello", too tired for formalities
noon is "high noon"
midnight is "the witching hour"
It depends on the context. I used to work night shifts during which I had to deal with the public. If I spoke to someone at 12.01am (0001hrs), I said "Good morning".
Remember - if you don't use correct capitalisation, punctuation and spacing, anything you write will be incorrect.