After making your curriculum purchases, it's possible you have just bought 19 kinds of curriculum, and yet the days remain just 24 hours long. In fact, I strongly encourage you to not overwork your teenagers. Consider not having them do school for more hours than an adult might go to work. Eight hours is a great number to consider a general, maximum number of hours.
How do you make sure you aren't overworking your children? Count the hours they might spend on each subject now!
Add up how many hours each curriculum represents. Can they get each thing done in a half hour? Or will it take an hour. When you are counting hours they might spend, consider these two key factors.
One hour of work does not mean perfect attentiveness.
Not 100% attentive.
Not slacking off either.
One hour of work is one hour of reasonable compliance
You and I aren't perfect, and in our daily lives we may want to be perfectly attentive to our job, but we really aren't. We hope that we will be reasonably attentive. That's what we can hope from our children too. Like you and I, our children are human.
When planning your curriculum for the year, consider how long each thing will take if your child works with reasonable compliance, not how quickly they will get it done when they are 100% attentive, but also not how long it will take if they are totally slacking off and distracted.
Count up the number of hours of work your curriculum represents! How many hours of school did you just purchase???? Should you cut back, perhaps?