We can clearly see that things changed after Paul's conversion and Christ's revelation to him of "the mystery". And so did Peter's words and understanding after meeting with Paul in Jerusalem and his own vision.
Absolutely. Do you think Paul, the Pharisee of Pharisees, who even though called to the Gentiles, would often go to the Synagogues before Acts 28, would write something like this during the time of transition?
Philippians 3:3 (AMP) - 3 For we [Christians] are the true circumcision, who worship God in spirit and by the Spirit of God and exult and glory and pride ourselves in Jesus Christ, and put no confidence or dependence [on what we are] in the flesh and on outward privileges and physical advantages and external appearances—
You can get preview of this in his earlier letters - Romans 2:29, 2 Corinthians 5:16, but now it is boldly proclaimed as Truth. The old religious divisions are set aside. He lists his former religious credentials, but counts them as rubbish compared to gaining Christ.
It seems this thread is heading in all sorts of directions that really are not necessary. The death and resurrection of Jesus Christ, and our faith in Him, was always primary in the transition time of Acts, and in this dispensation. During the time of Acts, Believers, especially the Jewish ones, were expecting the IMMEDIATE return of Jesus Christ and fulfillment of all OT prophecies. Paul was starting a ministry to Gentiles, not to become Jewish proselytes, but to become Believers in Jesus Christ. As of 70 AD, Israel ceased to be a nation. Their role as Light to the world ended - for now. The prophetic clock was paused. There had to be a new dispensation. Hopefully, everyone recognizes this most basic fact.
Outside of the destruction of Jerusalem, I don't believe there was a hard stop to the old dispensation. I believe there was a progressive revelation that accelerated pace as it became apparent that Israel, as a nation, had rejected the preaching of the Kingdom, and Jesus would not immediately return and reestablish the Kingdom of Israel - as everyone believed and scriptures foretold. The fact that it was approximately 40 years from the resurrection to the destruction of Jerusalem is an interesting coincidence. With Israel about to be set aside, God could now reveal a Mystery that was Hidden before, a plan to call out individuals who were both Jews and Gentiles into a new Spiritual Body with Jesus as the Head. Israel was a called out people from the nations of the Earth. The Body of Christ is made up of individuals from all nations with a Heavenly calling, with Jesus as the Head. The old religious divisions are gone.
If we knew the exact date that God allowed Paul to start teaching the Mystery, we could nail it down. Since we don't know that, we can only speculate. I lean towards the Acts 28 time frame - the last pronouncement to the Jews in Rome around 60 AD. It was about this time that Paul writes Ephesians, Philippians, and Colossians, the key books that reveal the Mystery. Ultimately, the timing does not matter. What matters is understanding what Paul taught in his later letters, and why the differences between what was taught and expected in the time of Acts, and what Paul teaches us who are living in this dispensation.
Since my time is limited on this forum, I'll give a couple examples.
Before Acts 28: Gentiles are blessed through Israel with Abraham. Its primarily an earthly blessing.
Galatians 3:9 (AMP) - 9 So then, those who are people of faith are blessed and made happy and favored by God [as partners in fellowship] with the believing and trusting Abraham.
Galatians 3:14 (AMP) - 14 To the end that through [their receiving] Christ Jesus, the blessing [promised] to Abraham might come upon the Gentiles, so that we through faith might [all] receive [the realization of] the promise of the [Holy] Spirit.
After Acts 28: Believers blessed in Christ with every SPIRITUAL Blessing, regardless of religious divisions. Its a Heavenly Blessing independent of Israel.
Ephesians 1:3 (AMP) - 3 May blessing (praise, laudation, and eulogy) be to the God and Father of our Lord Jesus Christ (the Messiah) Who has blessed us in Christ with every spiritual (given by the Holy Spirit) blessing in the heavenly realm!
Ephesians 2:6-7 (AMP) - 6 And He raised us up together with Him and made us sit down together [giving us joint seating with Him] in the heavenly sphere [by virtue of our being] in Christ Jesus (the Messiah, the Anointed One). 7 He did this that He might clearly demonstrate through the ages to come the immeasurable (limitless, surpassing) riches of His free grace (His unmerited favor) in [His] kindness and goodness of heart toward us in Christ Jesus.
Read Romans 11 where Paul is describing the Olive tree, where Gentile Believers were "grafted in", and the not so subtle warning of being broken off. This language sounds strange when compared to Paul's writings after Acts 28. The only thing that can explain this is timing. At the time of Romans, where the restoration of the Kingdom was expected immediately, this makes sense. After the destruction of Jerusalem, the dispersion, and the Revelation of the Mystery, not so much. Romans 11 will be relevant again during the Tribulation, when once again Israel takes their proper place as a Light to the nations.
Romans 11:17-20 (AMP) - 17 But if some of the branches were broken off, while you, a wild olive shoot, were grafted in among them to share the richness [of the root and sap] of the olive tree, 18 Do not boast over the branches and pride yourself at their expense. If you do boast and feel superior, remember it is not you that support the root, but the root [that supports] you. 19 You will say then, Branches were broken (pruned) off so that I might be grafted in! 20 That is true. But they were broken (pruned) off because of their unbelief (their lack of real faith), and you are established through faith [because you do believe]. So do not become proud and conceited, but rather stand in awe and be reverently afraid.
Compare that somewhat depressing Revelation, with the position the Believers now occupy IN Christ.
Philippians 3:20-21 (AMP) - 20 But we are citizens of the state (commonwealth, homeland) which is in heaven, and from it also we earnestly and patiently await [the coming of] the Lord Jesus Christ (the Messiah) [as] Savior, 21 Who will transform and fashion anew the body of our humiliation to conform to and be like the body of His glory and majesty, by exerting that power which enables Him even to subject everything to Himself.
Colossians 3:11 (AMP) - 11 [In this new creation all distinctions vanish.] There is no room for and there can be neither Greek nor Jew, circumcised nor uncircumcised, [nor difference between nations whether alien] barbarians or Scythians [who are the most savage of all], nor slave or free man; but Christ is all and in all [everything and everywhere, to all men, without distinction of person].
Colossians 1:12-14 (AMP) - 12 Giving thanks to the Father, Who has qualified and made us fit to share the portion which is the inheritance of the saints (God's holy people) in the Light. 13 [The Father] has delivered and drawn us to Himself out of the control and the dominion of darkness and has transferred us into the kingdom of the Son of His love, 14 In Whom we have our redemption through His blood, [which means] the forgiveness of our sins.
Ephesians 2:10-14 (AMP) - 10 For we are God's [own] handiwork (His workmanship), recreated in Christ Jesus, [born anew] that we may do those good works which God predestined (planned beforehand) for us [taking paths which He prepared ahead of time], that we should walk in them [living the good life which He prearranged and made ready for us to live]. 11 Therefore, remember that at one time you were Gentiles (heathens) in the flesh, called Uncircumcision by those who called themselves Circumcision, [itself a mere mark] in the flesh made by human hands. 12 [Remember] that you were at that time separated (living apart) from Christ [excluded from all part in Him], utterly estranged and outlawed from the rights of Israel as a nation, and strangers with no share in the sacred compacts of the [Messianic] promise [with no knowledge of or right in God's agreements, His covenants]. And you had no hope (no promise); you were in the world without God. 13 But now in Christ Jesus, you who once were [so] far away, through (by, in) the blood of Christ have been brought near. 14 For He is [Himself] our peace (our bond of unity and harmony). He has made us both [Jew and Gentile] one [body], and has broken down (destroyed, abolished) the hostile dividing wall between us,
If you can't see the differences between the Jew & Gentiles before the Revelation, and one Body seated in Heavenly places after, something is amiss.