Structuring Time

As one of my New Years modifications, I’m structuring my time in order to be more productive. This week I was quite productive: got our GDC plans sorted out, spent two days at CES, zeroed out my work inbox, and cleaned my place up a bit.
But over the course of the week, and now the weekend, what has occurred to me is the importance of unstructured time. Yes, I’ve been busy, and accomplished quite a few tasks from my to-do list. But the to-do list continues to grow in no relationship whatsoever to how quickly I work on its tasks. In fact, I could spend all my hours working on tasks on the list, and never actually stop to take a breath. Which is what has basically happened this week.
Now I’m on the weekend, working on a slightly different set of tasks, and I’m going to dive into this coming week feeling like all I’ve done is race. In the past, without structuring, it didn’t occur to me as race, it occurred to me as normality. But now, being more effective feels like a higher energy level, and I really need to spend some time in the lower energy level. So, unstructured time.
But how does that work out? Should I reward myself after working hard on a project for N hours? Should I just book in three or four hours and schedule it as “play time”? At what point have I “done enough”? I never actually feel like I’ve done enough, since I have so many things I want to do. I can see that figuring out how to schedule unscheduled time is just as much of a challenge as scheduling time for tasks.