How much study should a child do at one time: One hour, two, four, five hours; the answer to this question is simple. Each child has a different attention span, so work with your child while they are interested. If you notice that they are not paying attention take a break. The benefit of home schooling is that you are not constrained by time. Lessons can be intermittently throughout the day. I have found with my daughter that she has different attention span at different times of the day and prefers certain subjects.
We can be walking to get the mail and stop to examine an ant bed, and I explain how the ants carry food to their home etc, a science lesson on the way. My daughter counts the envelopes as she takes them from the mailbox, math. We sing the ABC’s as we walk back and there are some phonics and music. My daughter never felt like she was doing work. In the afternoon I read her stories as I put my baby down for a nap, and I tie another story in at bedtime for school work. So at the end of the day when the time is added up she has done nearly five hours of learning.