then i would consider it working hours, so the premise here seems to reduce to how much overtime i'm willing to spend.

I think there are are 2 situations here:

- I like [thing I do at my job] and I don't mind doing it outside of working hours. An incidental side benefit of this is I learn skills that enhance my career.

- A company I work for or am interviewing at is unhappy I don't like doing [thing I do there] outside of working hours, and either will fire me or not hire me unless I change.

The difference is "do companies use this as a metric", and I think it's pretty clear they shouldn't. If they do, they run into all kinds of other biases, mostly that you select out people who have family obligations (you're a parent, your partner also works, you have a sick family member, etc.).

Further, it creates a race to the bottom dynamic where a super important part of your life--your career--asks more and more from the other parts of your life. You shouldn't be able to get ahead of other people in your career by telling your kid to figure out algebra on their own, and if you can, people who advance in their careers (who will have more power in the workplace and thus society) will be the kinds of people who either had the resources to otherwise meet their other obligations (hire a tutor, nurse, etc.), or the kinds of people who didn't care about shirking them.

That's why maintaining this line is so important. It avoids an incentive structure that would empower the already privileged or the irresponsible.