I find David Allen's work most helpful here. He points out that more valuable than time is mental freedom. You can schedule all the time in the world to solve a

I find David Allen's work most helpful here. He points out that more valuable than time is mental freedom. You can schedule all the time in the world to solve a problem. If something else occupies your mind, progress may never come. On the other hand, if your mind is not preoccupied, finding the solution may take very little time. His practice in his book Getting Things Done helped me practice this, not just abstractly know it.