The regulations regarding home education are vague on the subject of full-time, but acknowledge that it doesn't have to match a school day. However, what is a full-time education? Certainly not the five hours a child spends in class each day at school. That's full-time attendance at school, but most people would agree that it doesn't equate to five hours of education. The actual useful education received during that time will vary by child, depending on many factors such as the child's interest in the subject matter, the teacher, other children, etc.
So let's look at an hour-long lesson in a school where children don't just remain in the same room all the time. Some time will be lost at the start of the lesson as children arrive from their previous class, possibly at slightly different times depending on how far they had to walk from the previous class and when they were released from that class. So the first five minutes are for settling down. The teacher will introduce the day's activities, possibly with a recap of the previous lesson, which takes another five minutes. Then we come to where the real education starts, the subject matter for the day. Typically there will be a mix of verbal explanation and visual aids, followed by the children doing their own work on the day's topic. At some point the children will complete the exercise, there will be time spent collecting and setting homework and the children will be packing up ready to leave for the next lesson. So in that hour, there could be as little as fifteen minutes of useful education.
This suggests that school is about 25% efficient, so that five hours of sitting in a classroom yields about one and a quarter hours of education for a typical child. The bright ones will no doubt receive less, and the less able will receive more. As regards on-on-one time, with thirty children in a class they can have no more than two minutes on average of the teacher's time in that hour. Then we come to school terms, which limit the official education to about forty weeks a year, which is 1,000 hours in the classroom and 250 hours of education.
Now, home educators don't really take long breaks because educating at home takes place at all times and even when on holiday there are opportunities for education. So, 250 hours in 365 days (yes, we educate at weekends too) is about 41 minutes of education a day to match the effective full-time education offered by state schools. Want a day off? Easy, just spend a bit longer each day for the next couple of days and the time is made up.