Why had the time to reach the Gentiles not yet come in Acts 3?
The time had not come because Israel, the favored covenant nation, was still dragging its feet and had not yet understood what God would accomplish through Christ's death, burial, and resurrection. God intended to use Israel to reach the pagan Gentiles at the appropriate time, but that time had not yet arrived.
Les explains that Peter and John in Acts 3 still lacked understanding of what God was going to put on the death, burial, and resurrection of Christ. They understood only that He was the Messiah, the Son of God, proved by His miracles, but they thought He was only for the nation of Israel. Yet God had not blanked the Gentiles out of His thinking. His plan was to use the favored nation, the covenant people, to reach out to the pagan, idolatrous Gentiles at the appropriate time. Because Israel as yet was dragging their feet, that time had not come. This fits the principle of Deuteronomy 29:29, that the secret things belong unto the Lord our God, who is sovereign and reveals things periodically.