The closer one gets to God, the fewer the words.
The Holy Spirit can only be partially expressed in human concepts. Anything we can say on this is unnecessary, and potentially misleading speculation.
Let us remember that it took the Fathers of the Church a great many years before they were able to commit anything specific to the concept of the Holy Spirit, and only under the strain of great contoversy. In fact, it was not uniquely the scriptures as such where we first learn of the Holy Spirit, it is in the prayers of the liturgy, the hymns and the baptismal formulae, which certainly predate the composition of the Gospels. They derive from the teachings of the Apostles themselves, and from them to Christ and the experience of Pentecost.
From the very beginning, baptisms have been done in the Name of the Father, the Son and the Holy Spirit. Yet many Christians were confused as to to fact of the Holy Spirit’s deity, so obscure to us this is.
The Spirit Proceeds from the Father, the Son is begotten of the Father, the Father is unbegotten and unproceeding. Anything we add to this formula has no purpose or meaning. “If the One was from the beginning, then the Three were so too.”
It has often been speculated in the past among early Christian apologists that the Holy spirit influenced pagans and Jews before the incarnation of Christ. Just as the Logos has been thought to have wrestled with Jacob, the Trinity has been thought to have visited Abram, and it has been argued the Holy Spirit influenced the pre-Christian world in it’s sparks of illumination.
The Incarnation of Christ (with the overpowering of the Holy Spirit upon Mary the virgin) was an episode in God’s plan for our salvation, so too the sending of the Paraclete upon Jesus return to the Father: an episode in the plan of salvation. The Holy Spirit is said to have been present with Jesus at the baptism in the Jordan, and with Jesus as the cloud around the Transfiguration. Since we know that God is truly transcendent, beyond time and place, these episodes are like intrusions into the created world, and do not indicate any sort of precedence.
To me these joint appearances of Jesus the Incarnate and the Holy Spirit are like one hand clasping another. There is a type of mutuality in the action of the Father, the Holy Spirit and the Son.
So anyway on a human timeline the starting point of the presence of the Holy Spirit was at least at the point of Incarnation, if not His presence as Triad with Abram. Possibly much, much earlier in ways that do not usually concern us.
The idea that the Holy Spirit might be eternally sent by the Son doesn’t work for us because it has the effect of placing the Holy Spirit in a subordinate position in the minds of we mortals, despite claims to the contrary. We may have witnessed the negative effects of this concept as it makes it’s way through the generations, the Holy Spirit is seriously neglected in the conciousness of many Christians, notably excepting the overemphasis by some Pentecostalists (who are probably reacting). It seems very difficult to find a balance in this devotion, and some people have gone to extremes in compensation.
In this day and age the idea of the Filioque has no meaning to people, not only adding words it increases confusion. It is a rump concept and needs to be dropped from the Creed we all share.