Good morning or Good afternoon or Good evening or Good night?

1. "Good morning" (Jap: "Ohayo gozaimasu") can be used for any time between midnight and noon, but
the times for "Good afternoon" (Jap:"Konnichiwa") and "Good evening" (Jap:"Konbanwa") are not exact. Generally,
"Good afternoon" is used between noon and sundown and "Good evening" is
used until it's completely dark.

2. The greeting after dark is a problem because "Good night" (Jap:"Oyasuminasai") is not a greeting:
its meaning is something like "Goodbye" (Jap:"Sayonara"). When people greet each other after
dark, they generally say something like "Hello".

3. When people say "Good morning" or "Good evening" in a very casual, friendly
way, they often say something that sounds like "G' mornin'" or "Gd evenin'"
with a kind of "muffled" or "reduced" pronunciation of "Good" and with a change
in the last sound of "morning" and "evening" (from the "ng" sound to the "n" sound).