How and at what point in time did Le'ah (Leah) become Ya'aqov's (Jacob's) wife?

Answer From The Annual Reading Schedule - Week 7 Notes For Genesis: Although Ya'aqov (Jacob) did not agree to marry Le'ah (Leah), because Ya'aqov was a man of integrity, she became his wife by default when he went into her. We learn from Exodus 22:16-17 and Deuteronomy 22:28-29 that the ruling is if a man goes into a woman he is supposed to take her to be his wife and he cannot put her away because he humbled her. This shows that as soon as a man goes into a woman, he has a responsibility and a debt to the woman's Father to pay the bride price and take her as wife. The Father, however, has a right to refuse. We can see that because the Father has this right to refuse in Exodus 22, the marriage is not final by the physical action alone, but only when the Father has found out about the situation and has an opportunity to express his disapproval of the marriage.

In the case of Ya'aqov, it is clear the Father (Lavan, also known as Laban) of the woman (Le'ah) did approve as he was the one who gave her to Ya'aqov. Therefore, the Father (Lavan) is aware of the situation and approves, so she (Le'ah) becomes his wife by default when Ya'aqov goes into her, even though he never agreed to this orally. The part of my answer above where I said, "because Ya'aqov was a man of integrity" is stated because after he found out it was Le'ah he did the right thing and did not refuse to keep Le'ah as his wife. I also consider it possible that the point in which he became married to Le'ah was when he found out it was her in the morning and did not try to give her back to Lavan. In a way, he kind of "agreed" to have her as a wife by not trying to give her back to Lavan in the morning when he found out. It is assumed in my answer above that because Ya'aqov was a man of integrity, as far as he was concerned, once he took a woman's virginity he knew he was to be her husband and would not try to avoid the responsibility of taking her as his wife.