Sometimes you'll only have 10 minutes to work on something. There should be a way of learning to turn on some intense concentration and getting something done. Don't say, "it's only 10 minutes so what could I do?"
On the other hand, there might be a fairly large window, like a national holiday on which you are snowed in and alone with your computer.
Windows of different size might have different functions, calling for different strategies. You shouldn't limit yourself to the standard sizes of 1-4 hours.