He was slain from the foundation of the world. In the fulness of time He died on the cross for all to see. So, payment for sin was already accomplished, before time began, in the eternal realm.
The Plan of God was that the Purpose of Christ's Sacrifice was only Determined Beforehand, from the foundation of the world.
Christ did not die twice. Not only is there zero evidence of this but the Scripture declares that Christ died only once.
For Christ has not entered the holy places made with hands,
which are copies of the true, but into heaven itself, now to appear in the presence of God for us; not that He should offer Himself often, as the high priest enters the Most Holy Place every year with blood of another—
He then would have had to suffer often since the foundation of the world;
but now, once at the end of the ages, He has appeared to put away sin by the sacrifice of Himself.
And as it is appointed for men to die once, but after this the judgment,
so Christ was offered once to bear the sins of many.
To those who eagerly wait for Him He will appear a second time, apart from sin, for salvation.
Hebrews 9:24-28