Find something you love to do and you’ll never have to work a day in your life.
— author unknown
I've spent a long time pursuing work I love, and one thing I can say unequivocally is that quote is full of shit. In fact, if anything, I've learned that doing what you love, far from making the work/life distinction irrelevant, makes it crucially important. Unlike if you have an office job, or even work that follows you home, when you do what you love, your work is your life, and that's enormously dangerous.
The biggest problem is not expecting it to feel like work. Long ago, I assumed that if I just let myself do whatever I wanted, I would naturally gravitate towards things I love to do. While this might be true in the large, it was a disaster in the small. There are too many small distractions and disturbances. I would wake up wanting to work on my project, but then I got an email that put me in a bad mood, or a new video game came out, or one of my housemates wanted to chat. Pow, day ruined. It took me a long time to realise that I needed more consistency.
So more recently I embraced habits, systems, and stability, all tools for producing consistency. As a result I've written 250,000+ words, produced nearly a hundred prototypes, and worked on a number of demos and other projects, almost entirely without external pressure. So it's fair to call it a success, I think.
But this, too, has flaws. I had longstanding reservations about stability and its effect on creativity, as well as the way obligation spreads and the feeling of never being done. In practical terms, my writing habit, which after a year and a half had devolved into repeatedly falling behind and catching up, finally lead me to accept defeat. A heavy blow, given that it was my longest running and, at least in raw output, most successful habit.
Ultimately, I think the source of these problems is that I had designed most if not all of these systems without any provision for not doing them. "Write every day" also meant making a sacrifice every day. Sometimes that sacrifice was small, other times it was big. Sometimes I wanted to write, and other times I was more or less forcing my hands onto the keyboard. In other words, it was hard work with no time off.
Okay, so don't work hard with no time off, news at 11. But behind every retroactively obvious solution is a problem-solving weakness worth learning from. You wouldn't think it would take me so long to figure out I needed a better work-life balance, and the fact that I did indicates some secondary problem that made this problem harder to solve. In this case, the secondary problem was believing that work I love would make balance less necessary. Unfortunately, if the work you love still feels like work (which I believe it must if you want to be consistent), then you still need time off from it.
Worse still, the power of habit isn't a magic bullet. A habit makes work easier, but you also have to put effort into maintaining the habit. Any time you get knocked off course and your habit falters, it requires extra effort to get back into it. That's still less effort in the long run, but only if your habits are fixed. But what if every time your habits stabilise, you add new ones? What if you do something really nuts and try a new habit each month? Habits can do a lot, but they are also work, and you also need time off from them.
Which brings me to the last question: what does time off look like when you do what you love? After all, isn't it the kind of thing you would do after hours if you had a different job? In fact, that's one of the reasons it's so easy to believe you don't need time off, because you would also do it for fun. But it's important to consider that doing the same thing for different reasons can lead to different results.
Your work is something you push yourself to do even if you don't feel like it at the time. It's something you strive towards as being greater than your transient moods or random distractions throughout the day. I've heard it said that truly great work performs itself through you, which seems like a good metaphor. You serve it, not the other way around. But that's exactly what makes it work, not leisure; you're optimising for the work, not for yourself. Of course, the work is what you love, but that doesn't mean it will always make you happy.
So time off when you're doing what you love is nothing more complex than forgetting all the rules and let yourself do whatever you want. Sure, maybe that means you'll spend the day coding anyway, but maybe you won't be in the right mood, or a new video game will have come out, or one of your housemates will want to chat. And that's okay too. After all, it's your time off, not from doing things you love, but from the discipline of doing them whether you feel like it or not.