We all have those moments when we're waiting on a phone call, only have 20 minutes until the next meeting, or have to "kill some time." It's difficult to be productive during those periods of limbo when you know you don't have enough time to finish a large task, and starting another one seems moot.
But begin to use those times wisely and you'll discover there are many tasks you can accomplish with just a few minutes here and there. Make a list of the jobs or responsibilities that can be accomplished in a short time. Then, when those limbo instances occur, pull out the list and get something done.
Also, when you have a medium chunk of time, don't waste it by hesitating. Leap at the opportunity to accomplish a 30 minute task when you only have 25 to spare. You'll be surprised at how quickly something can be done with total focus and limited time.