Whenever I offered working 66% of the regular office hours for 50% of my salary, my employer refused. Whenever I brought up I prefer other compensations than money e.g. cut working hours in interviews, I was promptly reminded that I will work with others and need to fit within the schedule, like off days, flexible work hours and part time work never existed. I only worked at one company that allowed parents to negotiate an early leave when they need to take care of the children.

edit: it applies to small local shops and 1000+ SF based companies too