Even if it was your job, 10 hours a day would be quite near-impossible I think.
I did 10 hours only once in my life. I got up at 9, got to the piano at 9:30 (without breakfast), and practiced until I noticed I was hungry, which was 3:30. I ate, relaxed, ate a small dinner, and went to the piano at 8:00, and continued to practice until exacty five minutes before midnight. My goal that day was to learn and memorize Chopin's Op. 10 No. 9 Etude, and 5 minutes before midnight, I did indeed play it through from memory.
It was fun, but it's nothing I'll probably ever repeat, let alone do on a consistant basis. Normally I practice 3 or 4 hours in a day. After 6 hours, I just get too exhausted to get anything done.