8-10 hours per day, plus another 1-3 hours for commute. Baby wakes up at 6:30, takes a bath and gets sleepy at 18:30 - so 12 hours of interactive time (not counting night-time feeding and crying) - and these 12 hours closely correspond to the fully-working parent's work and commute hours.

Yes, but then the working parent comes back and can parent

I didn’t say parenting only takes 8-10 hours. That’s the time the working parent works

That still leaves time to parent when off-work

8-10 hours a day, plus continuing education, networking, mentorship relationships, etc. ton not fall behind.