A lot of people are saying that my idea (to practice 5 hours straight) is not such a great idea. [I'm not gonna hunt down all the quotes, I need to sleep soon and I find it difficult to have time to post on the forum]
After all the reading, I suppose everyone is right. Practicing for so long for someone considerably inexperienced seems too rough and close to impossible to tolerate. I just - really desire to play piano. I want to be a pianist that can, with great prowess, share music with other people ; even though I may not be able to become a artist.. (my mother is not fond of the idea, after all I just started at 13 years.. not to mention they do not get good pay) I aspire to be a pianist that can.. it's really hard to explain, but the best way I can put it is to.. yeah I'll stop there

Basically, I want to play piano very well and share my feelings? with the audience.
Another theory - however foolish! - I am focusing too much on practice and should just enjoy the journey. Still, I want to be more than just an exceptional pianist - I want to play difficult songs because they are fun and enjoyable! But maybe that dream is only available to kids who start really young. How else could someone practice for so long and so productively?
Yes, I've read multiple books and articles and websites on deliberate/productive/systematic practice. I am still learning to deal with such tough, objective practice.
My question is, how can I slowly increase my ability to tolerate long periods of practice or just practicing a lot? Even if I have a lot of material to go through, after a while I just don't want to play. (mental exhaustion) Someone told me, when you are tired with practicing and you push harder to practice more is where you can increase your tolerance for practicing a lot. Is that even true?
@lostinidlewonder Time does go by when I practice, but when I mindfully practice, I can't tolerate practicing for more than hour/maybe 2 hours. I try to work on mindful practice and when I do work on repetitions, I focus on trying to make the repetition more better every time and I focus on the objective. Unlike Hanon exercises.. where you just cycle the hands through again and again. My repetitions, whenever I do them, are usually of measures that I have trouble on/etc, such as trills in Mozart's C Major Sonata.. (could really use advice on them. I tried forearm rotation, but can only achieve it with the left hand, which is irrelevant to the piece) It's a speed wall. So incorrect technique..
I do have good reason to practice a lot - I can always improve. That is my attitude (and it is in a positive matter, sorta ) When I fail to make the piece sound like I want - I can get a little frustrated. Anyone can relate?
I have digressed a little here and there, going off topic. Sorry about that.
Again, I'd like to show my appreciation for all the delightful and helpful answers.