Measuring work by time instead of by tasks accomplished is a major trap. It is relatively easy to see why this is so, but not so easy to correct the perception. After all, tasks do require time to be completed. More time spent productively will result in more work. The problem comes in the fact that nobody knows what an "hour's work" is supposed to look like. Is it a paragraph? A few random thoughts in one's head after having read something? A stack of papers graded? An hour-long seminar discussion? An hour's work could result in any one of these end-products. On the other hand, I do know what a paragraph looks like, an article, a book. I care about the product, not the process. Some hours are "better" than others.
If I could crack the nut of task management I wouldn't even need time management! Unless the key to task management is an especially savvy understanding of time itself?