The date of my baptism as an infant. Of course, I have had to cooperate with that grace along the way, and have backslid a couple of times. Some worse than others. We all have the capability of saying "no" to God's grace and salvation (free will), and I pray daily that I don't do or think something that would be saying "no" to Him. I have to trust that His mercy will protect me from myself.
Did He not make that decision before your were born?
Indeed before the foundation of the earth?
Or does that only apply to Mary?