I disagree about the "I only have one more hour to go then I can have a break," mentality being a bad thing. I say that to myself daily!

If I only practiced when I wanted to I would take a long time in reaching my goals. Piano is not my hobby, though. It's full time, so hence the more agressive attitude towards practice. However, I also do something else after I say that to myself. I follow it with, "what productive goal should I have, or what piece should I focus on for that hour." I try to not allow myself to "mindlessly" twiddle away that hour even though I wish I could be watching a movie instead!
To offset what I just said, I am not always a nazi about practicing. Like today for instance. Yes, I could do my last 2 hours of practice, but I had a lesson that ate up a good part of my usual practice time, I am trying to give my recovering arm a rest, and I plan to be diligent everyday next week if I can, so I totally just finished watching a movie! And sometimes I know that I just need a day off because I know that I am so not in the mood to practice that I don't think it would be very productive or enjoyable. But I can tell the difference between, "I don't want to," and "I REALLY TRULLY HONESTLY don't want to and need a break!" And I try to mainly cater to the later, though I have been know to give in to the first

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Long story, short, there is a time for work (even if we don't want to), and a time for play. And I agree, a schedule works wonders. I know a couple people doing/have done 6 hours a day, and they both were up at 5 or 6 in the morning and took a 1/2 hour break every 2 hours, and had all afternoon off being done at noon or 1pm at the latest.