When I was a SAHM and the DC were at school I spent maybe 2 hours a day on things like cleaning, shopping, sorting bills, cooking etc. And that was when everything was kept to a very high standard eg. spotless house, meal planning, everything that could be ironed was ironed, ridiculously thorough paperwork system. Plus if I had of worked hard and fast instead of dithering around slowly while listening to music or watching TV I could have cut that in half (as I now have to).
Then there were a few hours a week at the school, and a few hours volunteering elsewhere, plus some family commitments and a little bit of work I did for DH's business. Still, even in a busy week when some unplanned tasks or problems came up, unless the DC were sick and off school, I always had at least 10 hours a week during the day time that was completely my own. I read a ton, was up to date on all my favourite shows, caught up with friends, joined some different groups/took up a few hobbies...it was lovely. Probably the most relaxing period of my life as an adult.
Now that I'm working again I have an hour at night to read or watch TV (which I also did as a SAHM), and maybe a couple of hours to myself every second weekend or so if DH and the DC are otherwise occupied outside the home. As a SAHM just having 10-20 hours a week available to be at home alone was amazing, even if I was doing laundry. It's that part of it I really miss. But them I'm a major introvert.
I don't think it's knocking SAHM's by saying they have more free time if all the DC are in school. Surely that's part of the reason many people become SAHM's in the first place, less stress and juggling. That was a huge factor to me.