The phrase "Good evening" is typically said to greet someone in the evening, starting around 5:00 to 6:00 PM and continuing until midnight. It is used when meeting someone during this time and indicates the start of the evening interaction rather than a farewell. After midnight, especially during night shifts or early morning hours (12:00 AM to 4:00 AM), "Good evening" can also be appropriately used because it acknowledges the late hour. However, "Good night" is used as a farewell or when someone is going to sleep, not as a greeting. In summary:

• Use "Good evening" from around 5:00-6:00 PM until midnight as a greeting.
• Use "Good evening" after midnight if starting conversation (e.g., night shifts).
• Use "Good night" to say goodbye or before going to bed.

This guidance accommodates variations caused by daylight and context, with the key point being that "Good evening" is for greetings in the evening period, not late-night farewells.