Why Chinese fate prediction stopped at hours?

(Translated from here.)
I often had the question of why Chinese fate prediction stopped at the level of hours but not extending its coverage to minute or seconds? Why the logic which the fate prediction using birth time base on doesn't apply to minute or seconds? What scared status does these unit of time held? Since one criteria of validity of fate prediction would be differentiating different fate pattern of people born at different time, but it is simply illogical when that implies those who born at the same hour and same place share the same fate.
First that is due to the technological limit of time measurement at that time. Second is because Chinese had the idea of five elements from the year of birth, month of birth, day of birth and (double) hours which determine the destinate of individual which give us eight units. In according to 5 elements theory, one's life would be in perfect balance if an individual is birth at a time which 5 elements is distributed evenly among his/her year/month/day/hour. Since 8 is indivisible by 5, therefore the philosophical implication is that nobody born with a perfect life. Just like Freud assert that the ongoing conflict between ego, superego and id is what drive the personality development; Chinese also assume that there are inherent imbalance within each of us, and it is the imbalance/imperfectness drive the development of each person. Imbalance is what give birth to human psyche and society!