It should be mentioned, that there are two or three 'camps' of thought on the Am/Pm issue. I belong to those that believe only the so called day formula is the correct one for the Part of Fortune.
Also there have been some recent revelations/discoveries as to support a 'theory or belief', of the 'school' of Astrological beliefs and practices known as 'Esoteric Astrology' that is associated with the Theosophists, that being there is both an 'Evolutionary' and an "Involutionary' direction to proceeding through the Signs/degrees/Sabian Symbols of the Zodiac. What is the 'Evolutionary' is what has been extolled by the 'Esoterics' and is in reverse order to what all the rest [that, I know of...anyways.] of the Astrological schools are using.
I am presently working with a theory of mine that all Parts that call for a reversal of Parts formulae depending upon day or night really are only to be switched according to which 'cycle' one is applying them to and analyzing.
I've been blessed to have been introduced to and have had the opportunity to utilize the gifts of a top notch, clairvoyant, with a first rate reputation for her work, since 2003. I have, on a couple/few occasions, asked her to look into questions on Astrological questions/dilemmas . I did, in fact, ask her which of the two opinions, if either, was correct for the Part of Fortune. She said the 'day formula' is the only one to use for the Part of Fortune regardless of time of day.
The reverse formula is the Part of Spirit. Thus, so far from what I've been able to gather is that, what you find for the Sabian Symbol for the degree of the Zodiac the Part of Fortune is found in is symbolically representative of what you must be conscious of and be consciously applying to your life.
The Part of Spirit [sometimes called Part of Soul] is little used by Astrologers. I would say it is symbolically what one has to be aware of and apply to themselves as to achieving some measure of 'Spiritual' advancement.
Maybe my own situation can be a guide to you. My own Part of Soul is at 09* Aquarius 22' which has the Sabian Symbol of...[From Rudhyars' book on the Sabian Symbols]
"(AQUARIUS 10°): A MAN WHO HAD FOR A TIME BECOME THE EMBODIMENT OF A POPULAR IDEAL IS MADE TO REALIZE THAT AS A PERSON HE IS NOT THIS IDEAL.
KEYNOTE: The need to deal with human beings as persons rather than as screens upon which one projects one's dream and ideal.
Here we have a final statement on the relationship between mental-spiritual vision and living reality, between persons and the ideal they appear to incarnate..... ..... brings to our attention an issue that is basic and may confront us in various forms. Person versus archetype. This can mean a critical need for SELF-REVALUATION."
...it was in 2003 that at 50 years old my entire life was was turned upside down, over and around in so many ways that I just about struck dumb...kinda like catatonic from shell shock. In retrospect, I see it as a necessary cleansing/removal of past beliefs, attitudes and such. At that time the same aforementioned clairvoyant was introduced to me to hopefully be of some source of answer or understanding of situations , which she was. She also told me that I was about to become a writer and would be doing a lot of informative writing in that I'd be helping people to improve their lives...etc.
Well, I was a college drop out who took to construction trades [a Union trained Journey painter] and had just been badly injured at work [3 herniated discs] and got raped in the Workers Compensation trial/settlement [long story involving local corruption and dishonest lawyers.]. I'd been a half -hearted practitioner of yoga with a interest in Theology [comparative religions] of no achievements of any meritable mention. All in all just another John Doe with no where to go and going no where. So, I figured this clairvoyant was one of those that tries to tell you something wonderful is going to occur in your life to get you signed up for a few more readings ...meaning, she was just a scam out for the $$$s.
It turns out she's been right as to the essentials of what she predicted and where it would lead. From subsequent readings from her, [and from another highly reputable clairvoyant who told me the same thing], I was made to realize whom I had been in 3 past lives and that I was incarnate here again because of the work I was involved in [twice as a interpreter of the stars] and whom and what I had been in association with and in service too. That these associations were with and in service to beings and orders of spiritual knowledge and practices is exactly what I must now keep in mind and employ in my life as it does concern my soul...in fact it was told to me that this is at least the 6th incarnation I've been given in such a cause.
Whether or not you believe in re-incarnation and or anything else I just told you concerning myself...[I swear it to be the Truth at least as far as I know and can understand it ] the example I just gave of myself , my Part of Spirit and the accompanying story is a good base of understanding the difference.
If you are open to the idea, for added study and understanding you can also check what I and a number of others believe to have been the Part of Fortune for Jesus/Yeshua which is the 19th* of Pisces, the Sabian Symbol for which is [From Rudhyars' book]:
"(PISCES 19°): A MASTER INSTRUCTING HIS DISCIPLE.
KEYNOTE: The transfer of power and knowledge which keeps the original spiritual and creative Impulse of the cycle active and undeviated.
... and what we believe to have been the Part of Spirit for Jesus/Yeshua... which is the 14th* of Aries, the Sabian Symbol for which is: [again, from Rudhyars' book]
"(ARIES 14°): A SERPENT COILING NEAR A MAN AND A WOMAN.
KEYNOTE: Identification in bipolar relationship with the impersonal rhythm of natural energy.
The symbol for Phase 4 pictures a man and a woman in love walking together. At this new and more mentally stimulated level of experience and consciousness, a third factor appears: the serpent, whose coiling represents the spiral-like process of evolution - not merely "sex" according to the maker of cathartic symbols, Sigmund Freud. We can understand this "triangular" image — man, woman and the serpent — if we relate it to the preceding one in the series, the unexploded bomb of the anarchist or activist. The urge to blow up some structure which somehow has become in the activist's mind a symbol of the Establishment — the ruling elite — is usually the protest of an alienated and often immature mind that refuses relationship, because in the relationship he would occupy a subservient position. In this symbol, the serpent represents the acceptance of relationship by the two polarized human beings.
There must be a polarization before there can be fulfillment. The tragedy of so many contemporary lives is that, having become sharply individualized, the men and women cannot find their truly matching polar-opposite. Because they are not fulfilled at the root level of human emotions and vitalistic forces, they pass their lives seeking the ideal complement, often glamorized as the "soul mate." This search can find its expression at several levels. At the mystical level we have the examples of the "spiritual marriage" of Saint Francis of Assisi and Santa Clara, or recently of Sri Aurobindo and Mother Mira.
The Adam and Eve story (in Hebrew, Ish and Isha - much more significant names!) refers to this principle of polarization, although the story has been turned upside down by priestly intellects to serve their purposes. Adam and Eve accepted the Presence, not of the Tempter, but of the Individualizer, who sought to have them born out of the womb of unconscious passivity to Nature's God. But the result of the experience frightened them. They "hid"; they failed in the great test of individualization, and in this sense the archetype of that failure is deeply imbedded in man's generic unconscious. It is repeated time after time.
Modern "individuals" are confronted with another test, but they do not understand its meaning. It is the test of polarized conscious participation in the evolutionary process - a polarization that could dissolve alienation, isolation and egocentricity. In a sense at least, this was the old Tantric concept in India; but today many young people accept the concept only superficially and miss its real essence. They cannot understand the meaning of entering into the serpent, i.e. of developing eonic consciousness and that transpersonal living which once was characterized by the words: Not I live, but Christ lives me - Christ, whose symbolic number in Gnosticism is 888.
At this fourth stage of the third five-fold sequence, we are confronted with an image suggesting the transpersonal way to the "cosmification" of desire and the conscious acceptance of polarization as the solution of the problems generated by individualization. But this need not mean what is currently meant by "sex" and the glorification of the orgasm. It implies rather the RITUALIZATION OF RELATIONSHIP."