"Bonjour" means "hello", right? Why can't you say it at night?

In this video, I'm explaining the difference between "bonjour" and "bonsoir". Both are used to greet people but not a the same time of the day. Say "Bonjour" until the end of the afternoon and "bonsoir" once the evening starts. Bonjour is a greeting and only a greeting at the difference of "bonsoir" that can be used to say good bye in the evening and evening ONLY.