The other part of the recommendation is "at the office 5 days a week". Working more than 40 hours and spending meaningful time with your kids is very possible, if you aren't wasting 2 hours a day commuting and you have a flexible schedule and you have a partner who can also spend time with the kids.
> Working more than 40 hours
But he's also not recommending 40 hours, he's recommending 150% of that. Even then, I'd assume that when he says "sweet spot" he's also talking about a median, meaning you'll have to put in additional hours sometimes.