God knows the moment of our regeneration. Regeneration, of course, is the making alive or the quickening of our souls from death to life when we are made to be born again by the Spirit.
There are some instances in Scripture where it seems that we know when someone was regenerated, but we still don’t know the exact moment when that person was regenerated. The theologian Louis Berkhof is very helpful in talking about this in his Systematic Theology. That’s a good place to read on this subject.
So, no, we don’t know the moment of our regeneration, and in one sense we can’t really know. Can we know, perhaps, when we heard the gospel and trusted Christ for the first time? Yes, some people do know that, but many Christians do not.
I remember as a kid when I first heard the gospel. I think I was thirteen years old. My dad took me to hear an evangelist at Far Hills Baptist Church in Dayton, Ohio, and that was the first time I heard the gospel.
I don’t recall there being an invitation, but if there had been an invitation, I think I would have gone forward. Every time after that when I heard the gospel—whether it was at a campfire, a camp, or a Sunday morning in church—if the pastor or the teacher would give any sort of invitation, I would raise my hand. I came forward because I knew it was what I needed, but I still don’t know exactly when I first actually believed. But there are some Christians who do, and that’s a wonderful thing.