My DS is accelerated 5 years. Because of this, his homework is at times insane. I sat down with all of his teachers and made a deal. 30 minutes a class for a total possible 2.5 hours. Anything that doesn't get done gets pushed to the next day or to the weekend. He only has core classes 4 days a week, none on friday and it is very rare to have assigned homework that is meant for the weekend.
His teachers are clear that I monitor his homework time as he tends to screw off. So if something doesn't get turned in on time, they know it's because there was too much. He is not allowed to "spill" into the following week. So far it has worked although there are days that I wonder at the choices i've made.