The period of time language is controversial among Catholics. It COULD be an instantaneous process.
How do you construe this:
[2 Cor 3:18] And we all, with unveiled face, beholding the glory of the Lord, are being changed into his likeness from one degree of glory to another; for this comes from the Lord who is the Spirit.
you need to read all of chapter 3 of 2 Corinthians. The context of the piece is growing in the Lord (while alive) - sanctification, not about glorification. The person who lives with their focus on Jesus is what they are talking about, and how by doing this they are transformed from one level of glory to a higher level of glory, which is what the sanctification process (aka living our life as a Christian as best we can) does.
2 Corinthians 5:8 is validation enough that God completes our sanctification for us instantly when we die and our race is over: “We are confident, I say, and willing rather to be absent from the body, and to be present with the Lord.” The prior two verses 5:6-7 provide the context that validates this point of view.