Why couldn't the OT martyrs and righteous, along with the good thief, be released from limbo into Heaven at the moment Christ died on the cross?
My understanding is, that Christ has 3 roles to fulfill.
1) Redeemer - Christ's victory of the Cross and over sin, was not complete until the Resurrection, when He proved He was God.
2) High Priest - Christ's mission was not fulfilled until the Ascension, after He had instructed the Apostles and sanctified them as Bishops.
3) Savior - He did not reconcile mankind to God the Father, until He Ascended into Heaven and re-opened the gates. Christ is the only person who could repair Adam's sin and thus, it seems fitting that He would be the first person to enter Heaven, the "new, Spiritual Garden of Eden".
The Divine Sacrifice, alone, saves us, so did it not save and release them into Heaven at the moment of His Consummation?
Being saved from sin is not the same thing as being allowed into heaven. Redemption and Salvation are 2 different things. The Cross redeemed our sins; the Ascension gave us the possibility for salvation/heaven.
Again, Christ's Divine Naure always remained in Heaven while His Human Nature descended into limbo for three days.
I'm not sure where you're getting this idea. Sounds protestant.
The righteous were joined with Christ (His Divine Nature) in Heaven that same day. To me, that makes more sense than having to wait a bunch of days before Christ's physical body ascended into Heaven. Even with Christ's Human Incarnation on earth during those days/weeks before He ascended, He was also in Heaven. He had to be, for He is God.
Christ suspended the normal operation of His Divine nature while He was alive. And He can be in multiple places at once, for God is everywhere, always, forever. The fact remains that the gates of heaven being opened was related to "time" since salvation must be worked out on earth.
The Church teaches us that the gates of heaven were ONLY opened on Ascension Thursday, thus, we must hold to this strict account and assume no saints entered before Christ. Since they were already dead and no longer on earth, "waiting a bunch of days" doesn't mean anything because time doesn't exist in eternity.