Paul had intended to be in Jerusalem by the Passover but was prevented in doing so when a plot against his life was uncovered (Acts 20:3). His second plan was to be there by Pentecost (Acts 20:16). Obviously, he would have more time to spare on his journey than if his first plan was fruitful. Since he spent the winter months at Corinth (Acts 20:3; cp. 1Corinthians 16:6), he would have been ready to embark from there to the Province of Syria in late February or the first week in March. However, due to the plot on his life Paul spent three or four weeks journeying through Achaia and Macedonia visiting the churches there and didn’t set sail from Philippi until after the Days of Unleavened Bread (Acts 20:6).
The Feast of Weeks, as Pentecost is also called, is composed of seven weeks or Sabbaths plus one day making it fifty days after the day the Wave Sheaf Offering is made during the Days of Unleavened Bread. This particular day is always a Sunday, and upon that day the harvest is blessed for the rest of that year. It is also the day in which Jesus rose from the dead, blessing the harvest of souls for God. He is our Wave Sheaf Offering.
The first of the seven Sabbaths was spent in Troas (Acts 20:6-7), and Paul continued on his journey immediately after that Sabbath. Paul was traveling on a coast-hugging vessel, not the sea worthy sort he would have used to depart from Corinth to Syria (Acts 20:3). If we account for one day for Paul to journey from Troas to Assos and from there to sail to Mitylene, we may account for another three days to travel from Mitylene to Miletus, staying overnight at three of the four ports mentioned (Acts 20:15). Paul would then be able to send messengers to Ephesus to bring the elders of the church there to him at Miletus (one day traveling to Ephesus overland and one day to return to Miletus, see Acts 20:16-17). In doing so Paul would have spent the second of seven Sabbaths at Miletus, preaching his farewell address to the church leaders (Acts 20:16-38). Originally, Paul may have intended to spend a longer time with them, if he was able to set sail on the larger ship as he intended in the beginning (Acts 20:3; cp. Acts 18:18-21).
Another three days was spent port hopping before Paul was able to arrive at Patria (Acts 21:1). Since Paul and company was probably also packing grain harvested in the gentile churches for the poor at Jerusalem (cp. Acts 21:15), they may have spent another day unloading from one vessel to another at Patria. The oversea voyage took five days, so Paul would have spent the third of seven Sabbaths on board the large vessel on the way to Syria, possibly marked by Luke’s words “when we had discovered Cyprus, we left it on the left hand, and sailed into Syria.” Paul and company finished the week at Tyre by celebrating the fourth of seven Sabbaths with some brethren (Acts 21:4), which Paul no doubt had ministered to while his ministry was headquartered at Antioch during the days when he and Barnabas were together.
Paul then embarked for Ptolemais and spent one day there (Acts 21:7) with the brethren and then set sail for Caesarea, where he spent many days with Philip, who was one of the Seven of Acts 6 (Acts 21:8). It was here that Paul spent the fifth of the seven Sabbaths counting to Pentecost.The many days in Acts 21:10 probably means over a week before they took their journey to Jerusalem (Acts 21:15), leaving a few days following the fifth Sabbath. He could not have stayed much longer than nine or ten days and till have concluded his journey to Jerusalem before Pentecost. The same Greek phrase, translated many days, is used at Acts 16 18 for the time Paul endured the ‘help’ given him by the slave girl possessed by divining spirit. I cannot imagine Paul enduring such behavior longer than a few days. So Paul probably spent two or three days after the fifth Sabbath counting toward Pentecost with Philip and took his two day journey from Caesarea to Jerusalem after ‘those days’ (Acts 21:15).
Paul arrived in Jerusalem and spent one day there before meeting with James, the brother of the Lord on the second day (Acts 21:17-18). He then spent another several days at Jerusalem undergoing the purification rites demanded by the Law, as he was to pay the sacrificial expenses for several Jewish Messianics who had a vow (cp. Acts 21:23-24, 26-27), and this would have certainly incorporated another Sabbath day. It was near the end of this ceremony, sometime after the sixth of seven Sabbaths before Pentecost, that Paul was recognized by Jews from Asia and falsely accused of desecrating the Temple (Acts 21:27).
Paul, therefore, was seized by the Jews in an effort to kill him sometime during the final week before Pentecost. The day after his arrest Paul was set before the Jewish council by the Roman tribune in an effort to establish why he was taken by them to be killed (Acts 22:30). Failing this and after one more day, Paul was sent to Caesarea due to an exposed secret threat on his life. Since Paul’s journey from Jerusalem to Caesarea took no more than two days (Acts 23:31-32), but it took the high priest and company five days to take the same journey (Acts 24:1), I conclude that the high priest waited until the Pentecost feast day was over before embarking on the two day journey. If he desired, Ananias, the high priest (also known as Annas) could have been in Caesarea on the day after Paul arrived there, but the text concludes Paul waited in Caesarea at least three days, possibly five (depending upon when you begin the five days), before the high priest arrived. In any event, Paul undoubtedly spent the seventh of seven Sabbaths and Pentecost Day at Caesarea under house arrest. This accounts for Paul’s time spent on his final journey to Jerusalem after his third recorded missionary journey.
 See F.F. Bruce, The Book of Acts, page 421, citing Chrysostom (Homily xlv.2).
 I argued earlier that it is inconceivable for Paul to leisurely spend a whole week in one city when he had so many people to see before arriving at Jerusalem by Pentecost. Sea travel was inconsistent, not knowing when a storm would keep a vessel in harbor or hinder otherwise one’s progress. The land travel from Caesarea to Jerusalem was more predictable, so Paul could spend more time with brethren there than at any of the other locations when he would need to use ships for traveling. The “tarried there seven days” at Acts 21:4 should be understood as Paul and company ‘continued’ there or ‘completed’ the seven days there. In other words the fourth week, counting to Pentecost, which began aboard ship was completed by celebrating the fourth Sabbath with the brethren at Tyre.