saborfang17 - Think of it like weight training. If you want to develop your chest, you do bench presses. But if you do them until you're exhausted on Monday, then go back and do it again on Tuesday, and Wednesday, so on so forth, you won't grow much muscle. You'll just tear up what you already have and possibly injure yourself. Same thing with your brain. If you do a move 8 or 10 hours a day (which I have heard of), you're not going to learn it any faster than if you do it maybe an hour or half an hour then stop, and in fact you might slow yourself down.
I'm not saying that you're guaranteed to improve no matter what as long as you don't over work the brain, but you're more likely to improve if you practice intelligently. That means you work on something for a while, then you set it aside and work on something else. The brain does a lot of processing in the background that you don't even know about.
A couple fun facts, as well. A short nap will improve retention of information. Meaning if you practice for a while, then rest or sleep for about an hour, you're going to process the information and store it more efficiently than if you stay up and keep busy.
Also, people can learn physical skills just by imagining doing them. Meaning if you think about what you're doing with the sleight, and just visualize the movements of your hands or whatever (without anything actually in your hands) your brain doesn't know the difference that well. You can improve your skill just by doing that. You still need to practice, of course, but it helps a lot.
Lastly, remember that a second nature habit is very difficult to break. It takes 10,000 hours to make something second nature, but it takes 20,000 hours to break that habit.
JB - Videoing myself has helped me so much. For me, though, it was the opposite. A lot of times I think I'm terrible at a sleight and I'm not improving at all. Then I record it and realize that I'm actually doing pretty well and it gives me confidence. Nothing quite gives the spectator POV like a camera.
Unfortunately I no longer have access to one, so I haven't been able to record any of my actual performances for review.