I took a shower and kept thinking about this:
The real issue isn't finding what X hours is for everyone (futile), but employers who force or pressure people to work beyond their comfort or ability. This is why work/life balance is the #1 most selected tag on @keyvaluesio.
The goal isn't to determine how many hours other people should work. Just focus on finding folks who accept and support you in your current chapter of life. If you're an employer, this means creating a workplace that accommodates the constantly changing needs of your employees.