I have heard a story of a woman who was pregnant, i belief for about a month, and she was a bit worried. Some day in bath she saw how a small light came towards her and entered her belly. She immedialtely knew she ‘received’ a boy and her worries about the pregnance were gone.
Therefor i was wondering if this timescale of the gandhabba entering the womb really is a few days or might even be longer.
Although i do not question the experience of the woman, ‘a descending gandhabba’ feels for me a little bit as an animistic belief, quit primitive. I also read the Brahmins had this idea. So maybe the Buddha copied this idea of the Brahmins.
I do not know if we must take such images as ‘a descending gandhabba’ literally. I am quit sure you think we must, but i do not exclude the Buddha can have made use of such images as a descending gandhabba as a easy means for a much more complex process of rebirth.