Heidegger's Bible Handbook: Ruth: The Chronology of Ruth
4. The chronology of the same. The history falls in the time of Ehud or Shamgar, about one hundred and twenty-eight years after the entrance into Canaan.
As far as the chronology is concerned, it is not plainly evident in what time the history of Ruth happens: and the judgments of the learned concerning it vary. Now, those that push her back into the time of Ehud, or at least of Shamgar, who succeeded the former, and so insert her between the third and fourth chapter of Judges, to us do not appear completely miss the mark. And indeed, soon after the entrance into the land of Canaan, Salmon begat Boaz of Rahab, and Boaz begat Obed of Ruth, Obed begat Jesse, and Jesse begat David the king, Matthew 1:5, 6; Ruth 4:21, 22. Moreover, when Boaz took Ruth in marriage, he was older, Ruth 3:10; but Jesse, of all the men that lived in the time of Saul, was the oldest, 1 Samuel 17:12. And it is necessary that all those Fathers mentioned were old men, when they begat sons. For, since at the entrance of the four hundred and eightieth year from the exodus out of Egypt, and of the fourth of the Kingdom of Solomon, the foundations of the Temple were laid (1 Kings 6:1), with the forty years accomplished in the desert removed from the sum, and seventy years of the life of David (2 Samuel 5:4), and three of the Kingdom of Solomon, three hundred and sixty-six remain from the entrance into the land to the birth of David. Which three hundred and sixty-six years are thus commodiously distributed: in the forty-second year after the entrance into the land of Canaan, Rahab begat Boaz; Boaz begat Obed of Ruth in his one hundred and second year of his age (and so about the time of Shamgar, who succeeded Ehud in the one hundred and twenty-eighth year after the entrance into the land of Canaan, as the reckoning of the time described above convinces): Obed begat Jesse in his one hundred and eleventh year: Jesse begat David in his one hundred and eleventh year also. That these years of παιδαγονίας/child-begetting, although late, ought not to appear strange, the Most Celebrated Ussher of Armagh demonstrates in his Chronologia Sacra, pages 201 and following.