I perfectly understand what you said, yet I believe that practicing for five hours or so is not very productive. Now I'm no expert in the guitar, yet I do understand how the brain functions (I have two friends who went to Berkley and took some lessons, one of which stressed this point). If you are still beginning to learn the guitar, I would not recommend a five hour session for several reasons. First, your brain will get incredibly tired, and it does not happen only in music, it happens in almost every other aspect of your daily life, thereby reducing your productivity. Second, since your brain will get tired, then you will start making errors that may hinder your progress, especially in the basics learning phase. Third, you may get a bit tired of the guitar; I do not mean that the enthusiam wont come back, yet you will loose some time while you get the interest back (strange thing this one). In the end, we are not all professionals, (say as the Beatles who would practice for 8 straight hours a day) take your time, learn things one at a time and take some breaks. You will come with a less stressed brain back to the guitar.