In comments on the post below, Gyan has suggested that a "modern conception" of the Harrowing of Hell recognizes that, since it "is a supernatural event, it is outside our space-time and can not be properly said to precede or succeed any event in our space-time"; and that the Pope's answer to the question, "What is Jesus doing in the time between His death and resurrection?," follows this modern conception.
As a rule, I take the broad, flexible outlook on suggestions that relationships between the various states of existence are more complex than we might think. But try as I might, I can't quite square Gyan's suggestion -- which sounds harmless enough in C.S. Lewis's formulation, "all the moments are in this moment" -- with Church teaching.
Specifically, the Church teaching that divides human history into three eras:
From the creation of man to the Fall: Death had not yet entered the world.
From the Fall to Jesus' death on the Cross: The souls of all who died went to Hell, where righteous and unrighteous alike were deprived of the vision of God.
From Jesus' Resurrection until His return: The souls of the righteous are purified, if necessary, and then enter into the presence of God. The souls of the unrighteous go to Hell.
The dogma of Jesus' descent into Hell teaches us that Jesus' soul experienced the same fate as those who had died before Him, but that He then led the righteous souls, who through Adam's sin were bound to await their Redeemer without being able to see the Face of God, to Heaven. (And of course the dogma of the Second Coming finishes the story with the Final Judgment, confirming the eternal destiny of each of us.)
If the above is true, then it can't be true that Jesus' descent into Hell led the souls of all the righteous, from the creation of man through the Second Coming, from Hell into the presence of the Living God. Moreover, this notion that "all the moments are in this moment" is profoundly contrary to the Easter message that death has been defeated and that we -- as we live and walk about and eat chocolate -- are already redeemed.
Moreover, I don't think we can even say that the credal statement "He descended to the dead" can refer to both the traditional doctrine of Jesus meeting souls in Hell and the encounter Jesus has with the souls of the righteous who die after He rose. I say this because, as I mentioned above, the Creed refers to the fact that Jesus was dead when He descended to the dead, and now He is Risen. The difference between "dead" and "living" is simply too great to support that broad and flexible of a reading.