It's definitely possible.
I'm a sophomore and am taking six honors courses and maintaining a 4.3 GPA right now. I wake up to feed and take care of five horses at five in the morning and come home after school to do stalls for the second time and ride my four. Four days a week I also go to the boarding barn to ride my two reiners.
Homework/studying time is pretty much between 6 and 10. It CAN be done, but it's tough, and it wears on you.