When addressing an audience at night, is it generally popular to say konnichiwa? I've heard some Japanese singers use konnichiwa in the evenings when greeting an audience. Ordinarily I've been taught to use konbanwa at night. As a performer myself, I will be addressing a small audience in the near future, at 9pm at night. Should I use konbonwa or konnichiwa to greet them?

I have never heard of such a rule. I did a quick google search and found nothing relevant. I believe you can simply use konbanwa.

In the showbiz industry, it is common to use ohayo-gozaimasu (not konbanwa) regardless of the time of day (google " " if you're curious), but this is customary only when both people are in the showbiz industry. This has little to do with your situation where you're greeting your audience.