LOL!
Autonomous education doesn't start and end 9-3 pm (actually I don't believe the education of any child does, they are all learning all the time)
It's just that autonomous home educators, don't differentiate life from learning.
So just say to your dad that you don't limit your children's learning to school hours and term time any more.
Without knocking school as a valid choice for many families, it may help to point out to him, how much time in school is spent in crowd control.
Think of a lesson starting, how long does it take to get 35 children settled, how long does it take to make sure that 35 children remember what was covered last time, how long does it take to make sure the slowest member of the class understands the point of the lesson.
I don't know where, but somewhere I've read that a child gets an average of 18 mins a week, individual attention in state school.
It didn't happen every day thank goodness, but over the ten years of our children's home ed, I have been woken quite early with someone asking about the capital of Pakistan and the different factions in the Muslim religion. And I clearly remember one night getting quite 'romantic' with dh in our bedroom about 11pm one night and dd2 coming in saying "tell me about polysaccharide, I have been reading this book and need you to help me to understand them"..............
so yes tell your dad, it starts each day when they wake up and ends each day when they fall asleep, and is therefore way above the 25 hours or so that children get in school and therefore counts as full time education, AND we score much higher in individual attention time.