Executive dysfunction advice request: It takes me 8 hours to do 4 hours worth of studying. How do I reduce this time?

I'm looking to save myself some time. At present, it takes me about 8 hours to do 4 hours worth of studying. My goal is to get that time down to maybe 5.5 hours, hopefully less.

Any tips for managing executive dysfunction? Creating those 3 extra hours in a day could do a lot for me.