Where/when did God "reveal life begins at conception "?
In Genesis and throughout the text.
You have to read carefully and critically, and remember that God is the author, and God speaks precisely.
Go to the table of nations, whereby the descendants of Adam and his sons are described.
Read how lives are described: Adam begat Seth. Seth begat..., Methuselah begat..., etc.
When God revealed the distant origins of mankind to the writers of Scripture, he did so speaking in terms of chains of family linkage down through the ages.
By doing so, he showed that all of mankind everywhere on earth are, at root, first cousins (however many times removed). All of the people we kill in war, then, are our own family, LITERALLY.
Now, look carefully at how God revealed the lineages. He did so through the MALE principles. A woman bears a baby over the course of nine months, then gives birth, but a MAN begets a child at one specific instant, when his sperm joins with the egg to conceive a baby.
The male has no further part to play in reproduction other than that begetting. Begetting is not the sex act, for not every sex act results in a child. Indeed, most do not. Begetting by a male is the specific point where the MALE principles brings a child into being, and that only occurs at precisely one moment in a child's life: conception.
A woman bears a child over the course of 40 weeks, but a man begets a child at the moment of conception only, and is thereafter no longer NECESSARILY involved in that child's existence.
Every life in the Bible, including the life of Jesus, is measured from the moment of its BEGETTING, by the FATHER not its BIRTH from the Mother.
The Bible is inspired by God, and God knew what he was doing when he decided to pin human life to the MALE begetting, because that is a single precise moment, and no other. Female childbearing is long, but male childbearing occurs only at one instant: fertilization. That is begetting. And God revealed all human lives in the Bible as beginning at the FATHER'S begetting, which is conception.
That is where.