I'll give you good guidelines for how much time is reasonable, but flexiblity is the key. If you child gets math in a snap, good for them, they may not need forty five minutes and thirty will do. 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. I have just as much private time as I did when my kids were in school. I do the dishes and laundry during verbal math drills and when they are studying spelling. I am working smarter and really enjoying being in control of my days. You may want to vary your days.