ranjit reading your post, yeah, napping is probably far better than going for a walk or a run for piano. When I'm working (e.g., doing analysis or writing) it's different because I'm doing something I'm already really good at, so the walk clears my head and helps me focus when I get back.
But piano learning is different, at least for me as an adult-beginner (no longer a beginner player).
Anyway, five hours a day is completely out of the realm of possibility for me regardless, so it's moot! ๐