When do we receive a soul?

I have been asked by a Methodist friend about the Roman Catholic Church’s teaching regarding when the soul joins human life. He told me he read in a magazine that the Roman Catholic Church once taught that the soul does not unite with human life until 20 week and was puzzled how the Church could have held such a position.
It is both of our beliefs that the Church’s position / teaching is that GOD’s Creation, human life, specifically in this case begins at conception. I never really considered the soul and if it was given by GOD at the moment of the union sperm and egg. What I am seeking is:
1.) An authoritative source such as the Catechism of the Catholic Church or a link to the Holy Sea teaching about when human life receives a soul.
2.) Has this teaching changed from Peter to now?
3.) Reference(s) to scripture
Thanks in advance for your help to know GOD’s teachings on this topic.
Craig Schiro

Donum Vitae:

…From the moment of conception, the life of every human being is to be respected in an absolute way because man is the only creature on earth that God has "wished for himself " and the spiritual soul of each man is “immediately created” by God; his whole being bears the image of the Creator. Human life is sacred because from its beginning it involves “the creative action of God” and it remains forever in a special relationship with the Creator, who is its sole end.

…Certainly no experimental datum can be in itself sufficient to bring us to the recognition of a spiritual soul; nevertheless, the conclusions of science regarding the human embryo provide a valuable indication for discerning by the use of reason a personal presence at the moment of this first appearance of a human life: how could a human individual not be a human person?

Catechism:

1703 Endowed with “a spiritual and immortal” soul, the human person is “the only creature on earth that God has willed for its own sake.” From his conception, he is destined for eternal beatitude.

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