Actually, I found it interesting that Brian Eno, in an interview a number of years ago, said that if you're 100% serious about making it in music, don't get a "day job". And I can see the logic in that, having tried MANY times to hit the balance between "day job" and music and finding that the "day job" demands more of you than your art...which already demands A LOT.
This won't get fixed for a long time...at least, not until people start to remember why the arts are important, and start demanding that they be properly funded.
I don't have any great hidden wisdom, but I do have a few years' experience working a "day job" while also pursuing music. I was able to leave my "day job" back in the winter. When I was working, it was always part time, and I lived on less while i was doing it. I also tried to not compare myself with other people who seem to have more time, energy, talent, or money. For me it comes down to knowing what you want to do and also the idea of, "do you have what you need and are you happy?" Some people have a day job and are able to be musically fulfilled; music may not be their primary source of income, but they have a good balance because they have what they need but are also able to do what they want in music and the rest of their lives. But if that's not what you want, then that won't be satisfying. Of course, if the day job is taking all the time and energy you need to make music, that's not really balanced either.
It takes a lot of hard work to make a living in any creative field, but if you're pushing yourself so hard that music feels like a job and the joy is gone (either you don't enjoy making music or you don't enjoy life in general), then that's not balanced in my opinion. Your music will be worse for it because it'll absorb all that negative energy, and if you're not enjoying making music then what's the point? (That'll probably spread to the rest of your life as well, and you'll end up sad and lonely and probably die in a hole somewhere).
I think the most important thing is to find a community that drives you to pursue your passion. I don't have any interest in making music personally, but I've always found I accomplish so much more and have much more drive when I'm working on a team or in a loose grouping. Just having the ability to show progress, receive feedback on that progress, and a little healthy competition can work wonders for turning your down-time into something you're proud of.