I spend about 20 minutes a night writing out the sheet of daily assignments for the third grader. Internet research for the next week is done on the weekends. We start anywhere from 9am to 10am, and then extend the day in the afternoon. My children helped make that decision, they prefer to sleep in. So, if you get up at 8am, you literally have an hour to two hours to do what you want to do.
Lunch is another hour break.
Mid afternoon is another 20 minute break, but again, you extend YOUR time by assigning independent work right before or right after the break. Commitment means sticking to a task. There are many days when we don't finish everything, and I try to do it as homework that night. You may find that approach will keep your kids from contributing. Homeschooling also means that you can give your kids a break when they are feeling bad with colds, tired, etc.