This question already has an answer here:
I was at this supermarket near my university about 20H30. When the person at the counter starts billing my purchase, zhe said bonjour when I was expecting a bonsoir. My response was an immediate bonsoir (by the books!), and I felt it made them a bit uneasy.
Again, once at the fish market in the same supermarket, another person greeted with me bonjour, this time I replied salut which was a desperado attempt. Both incidents was in the middle of December night, about 20H30.
Is it fine to wish someone bonjour in the night? If so what would be an appropriate reply?
Addendum 1 - This situation is not a synonym to unclear time scenario. This is rather an exception to the rule, than a confusing application.