I was thinking about times when I would go to sleep at 11pm, and in what seemed to be 10 seconds later wake up at 3am to go to some wrestling tournament. Time seemed to pass in an instant, and this is because I wasn't "conscious".
When one undergoes surgery, often the surgery passes in what seems like an instant.
Now, we like to think of ourselves as being "conscious" when we are awake and "unconscious" while asleep in certain parts of the sleep cycle. But if you divide down further, is it not possible that we are conscious only, say, half of the time?
If you are conscious for 10 milliseconds, then unconscious for 10 milliseconds, and back and forth like that, it would be like being knocked out for surgery or dreamless sleep - but with one big difference: your world doesn't change much in 10 milliseconds. So to you, it would seem as if your consciousness was continuous, when really it was just a machine-gun.
As for time perception, the theory to be derived from this is obvious. As you grow older, perhaps the bursts of consciousness become shorter and the unconscious gaps become longer, resulting in the perception that time is passing faster.