Knowing when to quit anything is like questioning when to end a relationship. If you are even THINKING about the idea of quitting, it means you probably should. I've quit video games, I've quit pot, I've quit Reddit, I've quit social media, and many other things. When there is no value, and I start wasting time on something, the moment I ask myself; "Why am I wasting my time on this?" is generally the clear sign from the universe that it's actually time to quit whatever that thing is. Every time I've listened to that, and quit that thing, it's worked out great for me. If you aren't getting and reward or pleasure from it any more, it's definitely time to quit no matter what the excuses or justifications your brain will try to throw up in defense.