In my opinion, pointing out my own lack of a citation is a better practice than making uncited claims of fact. It's an invitation to prove me wrong, but the lack of a citation in itself doesn't make me wrong.
There's a difference between these three statements:
1. Women and men are different - obviously true and too vague to be meaningful.
2. Women have breasts while men do not - obviously true and mostly (and hopefully) irrelevant to this discussion.
3. Women work fewer hours than men - A specific claim about women that may be used by some to justify their prejudices against women. I don't doubt that you made the claim without malice, but unfortunately these are the kinds of remarks that reinforce sexist stereotypes. For this reason, I wish people wouldn't make such claims unless there is watertight evidence backing these claims.
"Women work fewer hours than men - A specific claim about women that may be used by some to justify their prejudices against women."
From my original comment: "Fortunately, there are far better indicators than gender of how prone an individual is to take extended leave." Choosing a man over a woman based on gender alone isn't just bad for society; it's poor reasoning.
The lower bound for men is zero.
Maybe it is zero for men who expect their wives to do all the parenting. It's certainly not zero for everyone else.
Objectively, his bounds make sense. You may not like what that data means, but that in and of itself doesn't make him sexist.
Women do often end up taking much more time off, but it is absolutely not clear that has anything to do with "breasts and uteri". I would argue it's cultural.