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Often she'd get an answer like, "Sixty, because I'm generally in the office from 8 to 8."
Then she'd ask: "How many hours did you work yesterday?"
Inevitably, she'd hear something like, "Oh, well, yesterday I was a little late. There was traffic. I went out to lunch with some friends. Yesterday I had to leave early because I had something at night."
Sixty hours, eh?
It's not, she learned, that people are deliberately tacking on a few extra work hours to their estimates. It's more that, when we answer the question, "How many hours do you work every week?", we've got in mind an image of a perfect day - one in which we really did log 12 hours straight.
Unfortunately, Vandkeram said when she visited the Business Insider office in October, most days aren't perfect. Meaning we generally work a lot less than we think we do.
Vanderkam is the author of several books including, most recently, "I Know How She Does It," in which she details what she gleaned from asking high-earning women to keep time logs for a few weeks (a total of 1,001 days for all the women).
In "I Know How She Does It," Vanderkam writes that she uses the "X - 25" rule to figure out how many hours people really work: If their estimate is higher than 75, subtract at least 25 hours.
In fact, when Vanderkam analyzed the time logs of those high-earning women (i.e. women who made more than $100,000 a year), she found that they worked an average of 44 hours a week, which is only about nine hours more than the average mother with a full-time job.
Other research suggests that, even if we are technically working 60 hours a week, much of that time isn't especially productive.
In 2015, I reported on research by Harvard Business School professor Robin Ely, who found that both men and women felt that work demands were placing a strain on their families, and were frustrated by inefficiencies in their work processes.
Ely concluded that being available almost round the clock can be a status symbol. In other words, we don't always need to hop back on email after the kids go to sleep - but doing just that can make us feel important.
Vanderkam's takeaway is that a "44-hour workweek, or even a 54-hour workweek, can make for a reasonable life." We have more time for ourselves and our families than we might think.
That doesn't mean, of course, that you're not working a lot, or working hard, or tired when you come home at the end of the day. But if you start from the acknowledgment that you're not working for all your waking hours, you can start being more mindful and intentional about spending the rest of that time in a way that's personally fulfilling.