Nehemiah was governor from the twentieth year to the thirty-second year of Artaxerxes the king, twelve years.
These references allow expositors to determine the precise time (and duration) when Nehemiah served as governor: from 445 to 433 BC. More importantly, the reference to the twentieth year
recalls the date mentioned in Nehemiah 2:1, when Nehemiah first laid his request concerning Jerusalem before the king and received permission to go and rebuild. Though the rebuilding took less than two months (Nehemiah 6:15), he remained as governor in Jerusalem a full twelve years.
14 Moreover, from the time that I was appointed to be their governor in the land of Judah, from the twentieth year to the thirty-second year of Artaxerxes the king, twelve years, neither I nor my brothers ate the food allowance of the governor.