I think that usage of these phrases may differ in American English as compared to British English. In American English: 1) “Good day” is rarely used by itself, but is commonly used when saying goodbye to someone: “Have a good [great] day!” I believe that “Good day” by itself may be used in British English in the “goodbye” situation. 2) “Good afternoon” in American English is only used as a greeting (when saying “hello”), not when saying “goodbye.”

In Canada, we do say "good day" as a greeting. It is not as common as "good morning" or "good afternoon". All three expressions would be a somewhat formal greeting between strangers or acquaintances passing on the street or in a retail setting as a way of acknowledging someone's presence. The expression "have a good day" would be used as a parting expression, perhaps in place of "nice talking to you". Hope this helps

good day means bye bye good afternoon is say Hi...greeting

good day means bye bye good afternoon is say Hi...greeting

good day means bye bye good afternoon is say Hi...greeting