I'm a SAHM, partner works from home full time, but it's very flexible apart from meetings, and he gets to do a lot of his own thing during work hours (on most days 4-5 hours to do his own thing).
I appreciate everyone's work Laod is different. In ideal world I would think four hours with baby is fair. Because you're each doing 8 hours. And divide the rest of the time in the day in halves.