Sounds like a recipe for burnout. I've tried a few times picking up a new language in my free time, but since I program for work it made my days feel 3 hours longer.
I've started picking up hobbies unrelated to programming, it's much easier to spend the time learning something completely different.
So when I said "work on something not work related", I didn't necessarily mean "creating a side-business". It could also be studying or something. In my specific case, I try to study a specific subject each week, for which I invest 4h per week. In fact, it doesn't even have to be technical, I just try to focus on something rather than reading bits and pieces about everything on HN, Twitter, etc.
I've started picking up hobbies unrelated to programming, it's much easier to spend the time learning something completely different.