While staying clear of that mental trap is key (so easy to forget, at least here in the US), I also think that for it to feel easy, some people have to make a conscious effort to make it easy.

If you're anything like me, any intellectually-gratifying side project I get started on will slowly consume me if I'm not careful. By that, I mean that it's what I'll think about when I get up, before I go to sleep and, yes, during all my free time. I can't do the one hour a day thing.

It's simply impossible to balance that state of mind with young children, at least the first few years, because it's not so much that they'd resent you if you chose to spend your free time on that side project instead of them (although if they're old enough, they will), it's that they physically need you for reassurance, feeding, diaper-changing, etc... That's a lesson I learned the hard way, especially after my second child.

A real danger for people like me is that you could end up resenting your own kid for depriving you of that intellectual gratification you crave. No matter how much fun little kids are (say < 4), they cannot satisfy that craving.