This means that the twentieth year of this king’s reign fell in or overlapped on 455 B.C.E. Based on this and other historical evidence the noted scholar Ernst Wm. Hengstenberg (1802-1869) in his Christology of the Old Testament, translated from the German by Reuel Keith, Volume 2, page 389, says: “The twentieth year of Artaxerxes is the year 455 before Christ. . . . ” And with this Archbishop Ussher and others agree.
The Watchtower Announcing Jehovah’s Kingdom. August 15, 1968 p. 504