While the Book of Changes can be considerably older, most scholars would agree that the Zhouyi (the Zhou book of changes) had existed for more than three thousand years. Throughout these three millennia, sages and the wise have had devised various methods or systems to predict the timing of future events.
Of these methods, the more popular and better known ones used to foretell the future or fate with certain accuracy are the Four Pillars of Destiny (Bazi), Wen Wang Bagua (Najia), the Purple Star Astrology (Ziwei Doshu) and the Plum Blossom Yi Numerology (Meihua Yishu). Many of these methods utilize a combination of the ancient system of Celestial stems and horary branches (devised by the Shang for their calendar) and the trigrams and hexagrams of the Zhouyi. In the hands of their founders (namely Chen Tuan and Shao Yong) and the real masters, predictions by these methods were amazingly accurate if not magical.
However Yi aficionados tend to use these derivative methods to predict the timing in Yi prognostications. If these systems work for them, well and good, if not then they could improve their own Yi studies if they just concentrate on what the ancients had indicated on how to read time, in the Ten Wings (the ancient commentaries to the Yi) instead of delving into various types of fortune telling. (It is not advisable for those who have less than ten years of Yi studies to read too deeply into the ten wings. They can easily get confused by the deep ancient thoughts and the cosmology contained therein.)
The Yi remains a book of wisdom and is to be used for divination purposes whenever required, but the Yi is never meant for fortune telling. Therefore it is incorrect for Yi students to mix up their Yi studies with fortune telling systems.
If one understands the ancients and the Ten Wings correctly, the timing in the Yi prognostications is provided in the trigrams and the twelve sovereign hexagrams and not from these much later derivative methods for time calculations. Steve Marshall has kindly provided a comprehensive depiction and explanations of the twelve sovereign hexagrams in his Yijing Dao website for Yi, Confucian and Dao students for their further studies. Perhaps readers can learn something about timing by reading his commentary on these hexagrams.
And if you ever come to realize why Shao Yong had numbered the eight trigrams the way that he did in his ‘Plum Blossom Yi Numerology’, perhaps like him, you have already read the ten wings thoroughly and understand something on how to read time into Yi prognostications. If not, then together, we still have lots to learn from the Yi and on the timing?