I apologies in advance for my answer being a bit off the beaten path.
Step 1. develop your brains ability to keep accurate time
- start simply with a digital stop watch
- wait until the time reaches on the minute (ex: 3:42:00 PM)
- now look away from the watch and try to look back at the watch when it reaches exactly 60 seconds later..WITHOUT COUNTING IN YOUR HEAD TO YOURSELF, just relax, do something else for the next minute, and your brain will 'trigger' you at approximately the right time
- continue practicing this until you have high accuracy.. and repeat over a number of days
Step 2. practice throughout the day predicting the time
- begin to translate your previously learned skill to predicting the precise time of the day
- without looking at a clock, guess the time.. again don't try to deduce the time, just relax and let the part of your brain that you developed in the first step take over
- this will take plenty of practice, but slowly develop your ability to predict within 10's of minutes (ex. you say its 3:15 and its actually 3:24), and then down to 5's of minutes, and finally down to single minutes
Step 3. experiment with short naps
- conduct the following two steps when you are healthy, and not exhausted (if those constraints do not apply, you brain can override your wish to practice in exchange for healthy sleep)
- before falling asleep stare at a clock and say the time to yourself
- say the time that you would like to wake up to yourself
- practice waking up at roughly the correct time
- if needed, practice with an alarm set to connect the skill of identifying the time with the ability to wake up
Step 4. begin to experiment at night
- on the weekends (when there is little penalty for making mistakes) repeat the previous steps, but sleep for normal amounts of time
Background: When I was young, I realized on occassions, I had the ability to wake up at times that I wanted without using an alarm clock. I developed this as I got older. When I was in college, I would frequently only have the ability to sleep for short amounts of time and actually routinely could take naps for as little as 5 minutes.
Now, because of my profession, I have the ability to sleep whenever and however long I want. I've used that situation to continue to refine my abilities to minimize the amount of sleep that I have, while maximizing my performance.
I frequently refer to the mass between my ears as 'my brain and I'... meaning the low level, inner workings, subconscience part as 'my brain' and the high level, conscience part as 'I'. I am happy to explain that 'we work together'. What I described in the previous steps is an example of this.