Someone asked the question "how does this apply to coding?" Yes, how would "hard practice time" apply to coding. Is that the time when you're actually head-down writing code? What about the time when you're not head-down, in your hard work and, for example, mulling how to get past a point where you're stuck? And is there an analogous activity for musicians - when they are not "hard practicing" but working through something in their minds?