To greet your friend at 10:30 pm, you will say

1. Time of day: "Good night" is generally used as a farewell greeting when it's late in the evening or nighttime, typically after sunset.

2. Rule for greetings:

- "Good morning" is typically used from dawn until noon.

- "Good afternoon" is used from noon until evening.

- "Good evening" is used from late afternoon until sunset.

- "Good night" is used as a farewell greeting during the evening and nighttime, often when saying goodbye before going to bed.

Given that it's 10:30 pm, "good night" is the appropriate greeting as it signals the end of the day and is commonly used in the late evening and nighttime.