The thief said "remember me WHEN you come into your kingdom..." Jesus replied "I say unto you today you SHALL be with me in paradise". And then John informs us that at Jesus' resurrection He said He had not yet been to paradise, had not yet gone to his father's throne.
Jesus does more than just remember the man at some point in the future, but instead tells the thief that he shall be counted among the righteous; not later, but today. Today the man is counted among the righteous and shall be among the righteous dead in Gan-Eden (aka Paradise, the place of the righteous dead; as opposed to Ge-Hinnom, the place of the wicked dead).
Christ's descent into Hades was the descent to the place of the righteous dead.
Paradise, here, isn't "heaven", but the place of the righteous dead.
Hades, the generic place of the dead, is described as consisting of both the place of the righteous dead, Paradise or Abraham's Bosom, or Gan-Eden; and also the place of the wicked dead called Gehenna from Ge-Hinnom.
Location isn't central here, as in Second Temple Judaism Paradise is also described as being in the "third heaven", of which there are seven. So, for example, St. Paul speaks of a man who saw Paradise in the third heaven--this corresponds with other Second Temple period Jewish literature, such as the apocalyptic portion of the book of Enoch where the eponymous Enoch is taken up and sees the Garden of Eden in the third heaven. This is not me advocating for the authority or truth of the book of Enoch, only presenting it in its proper historical context as representative of Second Temple Jewish literature.
When we read Scripture we need to look at it with ancient eyes, not modern ones. The things we read in the New Testament don't exist in a vacuum, but have real-world historic cultural and linguistic context. When Paul speaks of the "third heaven" he is speaking from an established Jewish context.
Jesus telling the thief that he would be with Jesus in paradise today needs to be read with ancient Jewish eyes: The thief will not have to suffer as a wicked man until the future Judgment, but is counted among the righteous, when Jesus descends to proclaim His victory over death, hell, and the devil the thief will be there with the patriarchs, prophets, and saints of old and shall be an heir to the gifts and promises of God which are in Christ.
It's not about the thief going directly to heaven (
per se), because you rightly note that Christ did not return to heaven until His Ascension, where He took up His seat of authority at the right hand of the Father. But neither does it mean that the thief must await for some eventuality, but is immediately reckoned righteous and shall be with Christ, as Christ has promised that "Where I am, you shall be also" to all who are His.
This means we need to get over some of our modern and western biases.
-CryptoLutheran