Quick light flicker, but on occasion and with limits?

I'm currently going through the Unity Learn courses, and while testing what I've learned so far by creating my own little project, I wanted to add something for fun; a light that quickly flickers on an off over a period of about 3 seconds utilizing my own "buzz" sound effect, but I only want it to happen once or so every 5-20 minutes. I can make a light flicker, but I'm having a difficult time figuring out how to constrain when it happens. For example, only after the light in question has been on at least 20 seconds, can't occur more than once every 5 minutes, but occurs at least once every 15 minutes, and can end with the light being either on or off. I understand I need to utilize Random.Range as well as Time.deltaTime to avoid using frames as a measurement, but as a total noob I'm having a hard time visualizing this in my head. If it helps, imagine the random light flickers in the title Phasmaphobia.

I'm trying to learn, I swear! I'm hoping that I can use any help to kind of reverse engineer and better understand how and why a script lets this happen.