Work/life balance is always a topic in vogue, and one of the key hallmarks of a “family friendly” company or profession is supposedly the availability of part-time jobs. From an economic standpoint, these are always difficult for companies to get their heads around, because overhead is similar for a part-timer and a full-timer (if these are professional jobs with benefits) and so hiring two part-timers is more expensive than hiring one full-timer.

But I would argue that the calculus doesn’t actually benefit families as much as people think it will, either. For starters, there are 168 hours in a week. That’s a lot of time. If you sleep 8 hours per night, that’s 56 hours per week, leaving 112 for other things. If you work 40 hours per week, that still leaves you 72 hours. That’s more than 10 hours per day — plenty of hours to spend quality time with your family, do your hobbies, exercise 30 minutes a day, and keep a reasonably well-functioning home. Even if you work 55 hours a week, that still leaves 57 hours, or a bit over 8 per day, for other things. For all that people talk of feeling time-starved, that feeling seldom takes those numbers into account.

Beyond that, though, data from the American Time Use Survey shows that when moms do work part-time, rather than full-time, on average, the hours aren’t necessarily gained in the way we think they would be. Moms who work (for pay) full-time spend about 36 hours per week doing their jobs; moms who work part-time spend 19. Moms who work full-time spend 8.40 hours interacting with or caring for their children; moms who work part-time spend 13.16. In other words, by working 17 fewer hours per week, you gain less than 5 hours of active kid time (the other extra hours are consumed by more housework, more leisure time — which is often spent watching TV, a few extra minutes of sleep, of shopping and other errands, and a larger chunk of unclassified time).

What’s even more interesting, though, is looking at what is done in those hours of interaction with children. Moms who work full-time spend a fairly lousy 0.04 hours (2.4 minutes) per day reading to their kids. But moms who work part-time only spend 4.8 minutes. Moms who work full-time spend 11.4 minutes playing or doing hobbies with their kids. Moms who work part-time play for 21.6 minutes. Moms who work full-time spend 6 minutes on education related activities with their kids; moms who work part-time spend 9.6 minutes.

In other words, in exchange for giving up a big chunk of income and often scaling down her career trajectory, the average woman who works part-time instead of full-time only gains, in practice, about 16 extra minutes per day in activities that most people would deem “quality time.”

Now, obviously, some people do much better. These statistics also include all married women with kids under age 18; for mothers with very young children the differences may be more pronounced. As it is, your 17-year-old doesn’t want to spend even 2.4 minutes reading with you (or 11 minutes doing hobbies together).

But, looking at these numbers, it strikes me that the hallmark of family friendly work is not so much part-time hours, it’s flexibility as to when those hours can be. If you can work a second shift from 8-11pm most nights, and your kids are in school, you can easily get those 36 hours of work-time in without serious non-family childcare. Over the past few years, I’ve interviewed moms of pre-school aged children who have flexible enough jobs to get in 10 hours during pre-school, 10 hours during naps, 10 hours on evenings and weekends, and another 10 hours when they have paid childcare. As with time at the office (see the previous post about wasted time at meetings and browsing the Internet), the question of whether we have enough time for things is more often about whether we are spending our time on the right things than anything else.