When meeting someone at 6:30 P.M., it is more appropriate to say "good evening" rather than "good night."
"Good evening" is used as a greeting in the late afternoon and early evening, typically from late afternoon until around 9 P.M. It is a polite and common way to acknowledge someone as you meet them during this time.
"Good night," on the other hand, is typically used when parting or saying goodbye to someone, especially as the night progresses and you are about to go to bed. It's a way of wishing someone a good night's rest or indicating that you are ending the interaction for the day.
So, in summary, if you are meeting someone at 6:30 P.M., "good evening" would be the appropriate greeting. Save "good night" for when you are saying goodbye or ending your interactions for the evening.