Now, how is this leettime calculated?
For a given humantime (e.g. 11:15 am) the value of the leettime corresponds to the number of times you have to add up 13 hours 37 minutes in order to exactly reach this time. Whenever the result overflows during the calculation (i.e. the obtained time exceeds 23:59 o'clock) you subtract 24 hours in order to stay on the clock.
Example: The leettime of 00:00 is 0, the leettime of 13:37 is 1 and leettime 2 corresponds to 03:14 am (because 13:37 plus 13 hours 37 minutes is 03:14 o'clock).
Is there a unique leettime for every humantime during the day?
Yes! There are exactly 24*60=1440 different leettimes, each corresponds to exactly one minute in the day.