What is the correct description of good morning/good evening/good afternoon, etc? Are they called greetings of the day, or time of the day greetings?
If not, what are they called?
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These are called phatic expressions, and their purpose is to perform a social function rather than to convey information. It's sometimes called small talk.
You might refer to these as good wishes, which is synonymous with greetings, regards, or (arcane) compliments. This wouldn't suggest that good wishes only covers the examples given in the question, but it can also include other phrases, such as "how do you do" or "how are you".
Good wishes certainly is a good cue to a child learning to pay his or her respect in a manner like this perhaps: "Remember to express your good wishes to Mr. Smith." It's not something you would commonly hear someone saying; but I do know people who do speak this way. Someone may say "Send Mr. Smith my good wishes." But even that sounds like a dated expression and "best wishes" is heard more often in this case.