Moment to Moment

Something has been puzzling me for a while now. What time does evening starts? When does an afternoon end? This started when I answered phonecalls between 5 pm – 6.30 pm. When I said “good afternoon”, the caller responded “good evening”. When I said “good evening”, the caller responded “good afternoon”. It happened a few times and I told myself that I have to find an answer to this. I don’t have any problem knowing when afternoon starts or when morning starts even though morning starts in the middle of the night.

Anyway, I googled to find the answer and found a few and one of them is this “6:pm starts evening. 6:pm until 12:am is evening. 12:am until 6:am is morning. 6:am until 12:pm is mid morning. 12:pm until 6:pm is afternoon. That's probably the official rule but theres no law against making it up to what suits you:)” from http://qna.live.com/ShowQuestion.aspx?qid=78127D0300574F85B437DA1358B6A724

But if I were to greet someone around 6 am to 12 pm, do I have to say “Good mid-morning”?
I just want to know whether I should greet someone “good afternoon” or “good evening” between 5 pm – 6.30 pm.