Does it matter to his salvation either way according to double predestination?
That's as clear as I can make my answer.
I think you are capable of a yes or no.
Did God know everything that would ever occur in time at the moment of creation?
I see you are still having trouble with the statement I keep making: "God is omniscient." Perhaps it is the word "omniscient." It means "all-seeing, all-knowing. Specifically to your question the answer is yes.
Does what matter? Your question is poorly stated.
Specifically to your question (Did God know everything that would ever occur in time at the moment of creation?) the answer is yes
Ahhh. Thank you. That wasn't so bad, was it?
Now if God knows today, knew on the day of your birth, has always known since time began, if you would or would not be joining Him in heaven, do you think there is any way you can change God's foreknowledge of that outcome?
Because if God "foreknows" something will occur, it seems to me that in order to be the sovereign Lord of all creation He says He is in Scripture, that whatever that "something" is will most certainly occur according to the omniscience of God.
Now Calvinists believe that God not only foresees the future, but that He ordains the future. But for now, we won't bother with that.
It's enough that you've admitted you believe that "God knows everything that would ever occur in time at the moment of creation."
So when you accuse Calvinists of saying a man's fate is already known to God and therefore set in stone, you are really challenging what you've already said you believe.
Man is separated from the beasts of the field only by his ability to know and choose right from wrong. Man is therefore capable of freely returning the gift of love to God.
In Calvin's universe man is only playing a role in some sort of kabuki theater, going through the motions, reciting his lines and then dying.