when

There is absolutely no question that Paul did repent (i.e., had a change of direction in his heart), as is clearly attested to in scripture. Therefore, the question being raised isn’t really an issue of exactly where (or when) this change within him may have occurred, other then how it relates to having occurred before or after his salvation. If his salvation preceded his repentance, then surely it must be attributed completely and entirely to God’s grace (and foreknowledge), given that Saul/Paul was a “chosen vessel.” (see Exodus 33:19;Acts 9:15.)

Peter spoke (to the whole house of Israel) on the day of Pentecost and instructed them to “repent and be saved.” However, Paul preaches a slightly different message that makes little to no mention of repentance being required as a condition of salvation, referring to his message of salvation by a new name, “the gospel of the grace of God.” (Acts 20:24.) In fact, Paul states that it is the goodness of God that leads one to repentance in Romans 2:4.

Or despisest thou the riches of his goodness and forbearance and
longsuffering; not knowing that the goodness of God leadeth thee to
repentance?

Repentance, at some point, is what God commands of all men (Acts 17:30)… but why is there so little mention of it in all of Paul’s epistles if it is thought to be a prerequisite to salvation?
Is it because the Gentile nations were not under the law (as Israel was) and would simply not relate to repentance in the same way that Israel did?

Romans 4

[15] Because the law worketh wrath: for where no law is, there is no
transgression. [16] Therefore it is of faith, that it might be by
grace…

This question has evolved from another question (that was downvoted twice, for reasons I do not understand) that is posted here:

When did Paul’s repentance (i.e., change of heart) and salvation occur? On the road to Damascus, or only after being baptized in Damascus?