Hi Hannah!
There is a Home Ed board here on Mumsnet which you might like to post on.
As cdwales says, conversation is one of the main ways that home educated kids learn. Because they are getting so much individual adult attention throughout the day, there is plenty of opportunity for that.
For this reason, HE parents don't tend to think of their children as being educated for a specific number of hours a day. Yes, you can get tutors in, but the kids' education doesn't end when the tutor leaves. You'll still find them engrossed in books about penguins, or experimenting with the trajectory of a bouncy ball, or getting into long discussions about how the bus company decides where the bus routes should go and how much to charge.
All that can be true of kids who go to school, of course. But they are more likely to be tired after a day at school, and sometimes tired of spending a large number of hours in directed educational activity. Often they need some down time doing something quite unrelated. For this reason, their parents are more likely to see a gulf between what are perceived to be "educational" activities, which usually happen during the hours assigned to school and homework, and "recreational" activities at other times.
In recognition of the fact that home education tends to create a different educational environment from school, government guidelines say that there are no fixed hours required. In fact, it isn't essential to do any formal academic "work" at all. In my family, we use an informal approach and I'd be very hard-pressed to say how many hours a day my children spend learning, just as I would be hard-pressed to tell you how many hours a day I spend parenting them. It isn't a discrete activity. It runs through everything. Does that make sense?