I'd guess that on average, men work more hours per year than women with the same jobs, because women tend to give birth and take care of children more than men.
I can't help but wonder if this is significantly influenced by an imbalance in compensation.
When my daughter was born, my wife and I decided that one of us would stay home, and income was certainly a large factor in determining that she would be the one to stay home. If our incomes had been reversed, then I would have become a stay-at-home dad.