No there's no time off. But come on. Some wives are grumpy no matter what...
What would all these parents do if heaven forbid their spouse had to leave and they had to take care of everything all the time all by themselves???
It happens everyday in the military. Men and Women leave everything behind and deploy for up to a year to serve their country.
Indeed, without a choice, you deal with it. However, you don't spend a lot of time doing things for yourself in that situation.
But when there are two parents, it is certainly not fair for one to say "you get all the kid duty - I'm going golfing." Thus, a trade is the fair way to work things out.