The efficiency of practice is the important thing. I find practice routines go up and down. For the last 5 days except one where I didn't touch a piano, I've been doing 10 hours a day.
I didvided it up and found that I can easily do it. Physically I'm fine, becasue I've been doing long hours for years now, and 2 hours of the 10 is nothing but technique work. The problems arise when you get to about 7 hours and you start to think umm, what should I do now? At that point do not learn new notes, just revise everything. I always set myself a schedule for the next day. Currently it is
1 hour pischna etudes, scales, cramer, czerny or summit etudy..
1 hour op10 chopin
1 hour Ondine
1 hour Beethoven 5th concerto
1 hour scarbo
1 hour op10 chopin
1 hour scarbo
1 hour beethoven 5
1 hour chopin op10
1 hour revising
I get up very early in the morning becasue I am not a very good sleeper so getting up doesn't bother me. I'm only working a lot at the moment becasue I have deadlines to meet and cannot fail to meet them.
Learning notes and stuff takes the time, once the tecnique is sorted, the hours cut down massivly. With no notes to learn I average 4-5 hours a day.
I agree a lot with mark737. It's amazing what sleep can achieve. But only if you sleep on good practice. Sleeping on bad practice is deadly. Bad practice and not achieving much is different though. I left today feeling like my scarbo is just never ever going to sound like I want, but I no that all the work I have done has helped it, and it's just me being impateint with it. If things are no better the next day, you have to seriously start asking yourself questions.