Occasionally we might start a little earlier, but not as a habit.
I myself was up that morning at five.

This was earlier than I had intended.

I had said to myself on going to sleep, "Six o'clock, sharp!" There are men I know who can wake themselves at any time to the minute.
They say to themselves literally, as they lay their heads upon the pillow, "Four-thirty," "Four-forty-five," or "Five-fifteen," as the case may be; and as the clock strikes they open their eyes.

It is very wonderful this; the more one dwells upon it, the greater the mystery grows.

Some Ego within us, acting quite independently of our conscious self, must be capable of counting the hours while we sleep.