There are no absolutes; they depend to a certain extent on the hours speaker and listener have kept recently and on the extent of daylight at the moment. However: Greetings upon meeting: good morning -- from waking up to noon (X) good noon -- not English good afternoon -- from noon till 6 PM good evening -- from 6 PM to 10 PM Greeting upon leaving: good evening -- from 6 PM to 10 PM good night -- from 6 PM to the wee hours.
New words, one handy idiom, and a 2-minute quiz — delivered to your inbox to keep your streak alive.