The definition of 100% capacity is arbitrary — no reason why it should stand at a 40-50 hour week. Actually, American society is more like an V8 with two dead spark plugs running at full throttle with nitrous injection. It may provide its rated HP output, but it’s liable to break the crankshaft or drop an exhaust valve soon enough.

Secondly, if you think about it, the current situation is unprecedented. 40 years ago, people married younger and the average family only had one working parent. Commutes were also shorter.

Assuming a 45-hour week including commuting for one parent, the average hours “worked” per parent were:
(45 + $housework) / 2

Now, assuming a 50-hour week including commuting for BOTH parents, we’re talking about…
(50 + 50 + $housework) / 2
$housework may be marginally less due to after-school day care in the second case, but not significantly less.

A 30-hour or 35-hour week per employee would more closely approximate the norm that prevailed from the 1910s through the mid 1970s while not locking one parent or the other out of having a career outside the home.