Lately in Chinese Metaphysic circle, there are many version of period 9. Some scholars insist that period 9 started in 2020, most Feng Shui Masters and Practitioners hold on to 2017 while the Flying Stars Experts stick to 2024.
The scholars that insist that period 9 started in 2020 is related or backed by the Saturn and Jupiter conjuction. This is an astronomy phenomenon that occurs once every 19.85 years (approx. 20 years). I’ve wrote something on this while researching into the Interplanetary Alignment of Xuan Kong Flying Stars, as far as this reasoning goes, it can be backed by science observation. And the Great Planetary Conjunction will occurs in 2040 which is 4 years faster than 2044 as transcibe in other Feng Shui theory and practice.
My personal observation (since 2020) is that this alignment planetary influences human behaviour more than Feng Shui. A shift in worldview among human beings, towards more period 9 phenomenon such as technology, media, internet, where appearance take precedence over substance, getting more ‘likes’ and ‘shares’ are more vital than substance; and female focus workforce (i.e. female senior management in corporate setting).
The Feng Shui Masters and Practitioners that hold dearly to 2017 is due to Xuan Kong Feng Shui, particularly in the application of Xuan Kong Liu Fa (6 Methods) and Xuan Kong Da Gua. In these 2 method, the idea behind period comes from the various permutation between Yin and Yang Lines in a Gua. Actually, if one has use these methods for a while, will realise not much significant difference when you are using period 8 or 9. Because, both 8 & 9 are in the lower period (下元). But, deep down we (practitioners) know or is wary of the greater challenge when it switch from 9 to 1 (change from 下元 to 上元). I believe by then, during this transistion, not many practitioners and Master will be confident enough to apply XKLF and XKDG as the degree of error is much significant and adverse.
And for the Flying Stars experts that stick to 2024 as period 9. Bluntly put, flying stars is simply a divination method force fitted as Feng Shui method or application. If we trace back to Tai Yi Divination Method, you will see the synchronicity within. Therefore, 2024 as period 9, as far as divination is concern, the accuracy is grounded.
In summary, 2017 deals much with Feng Shui (Earth Luck) while 2020 relates and influences Human Behaviour (Human Luck) and 2024 has deep synchronicity with various method of divination (Heaven Luck). All 3 years (cut off) is correct but depends which aspect we are uisng them for.