1 Ne 1:4  the first year of the reign of Zedekiah

Daniel Ludlow writes, “Lehi and his family apparently fled from Jerusalem in ‘the first year of the reign of Zedekiah, king of Judah’ (1 Nephi 1:4, 2:1-4). According to the Bible (2 Chronicles 36:11), Zedekiah was twenty-one years old when he was made king over the kingdom of Judah by Nebuchadnezzar, the leader of the Babylonian empire. However, the exact date of Zedekiah's ascension to the throne is not mentioned in the Bible, although nearly all of the scholars agree it must have been within a few years of 600 B.C.” (A Companion to Your Study of the Book of Mormon, p. 89)

Although Lehi and his family left Jerusalem not long after this, Jerusalem was not besieged by the Babylonians for another nine years, And it came to pass in the ninth year of his reign, in the tenth month, in the tenth day of the month, that Nebuchadrezzar king of Babylon came, he and all his army against Jerusalem, and pitched against it, and built forts against it round about.  So the city was besieged unto the eleventh year of king Zedekiah. (Jer 52:4-5)  Later in chapter 52, Jeremiah describes the unfortunate fate of Zedekiah; his sons (all except for one who would later travel with his people, the Mulekites, to the promised land) were killed before his eyes, and then he had his eyes ‘put out.’ (Jer 52:8-11)