I think aeh posted some research on a recent thread about homework volumes citing 10 minutes total per year of grade as a rule of thumb

http://giftedissues.davidsongifted...._much_homework_should_my.html#Post211260

The volume of homework your DD is being given is outlandish. I didn't have 2 hours of work until senior year of high school.

What is to give light must endure burning.