According to an article by Robert Smith and Stephen Ricks, anciently a year not only did not begin when we today assume it should, but the beginning of the year had special importance. The Babylonian and Phoenician New Year was on the first day of the first month, but in the spring in Babylon and in the fall in Phoenicia! In ancient Israel and Judah, the New Year could come with either the beginning or ending of harvest season -- near either the vernal or autumnal equinox, i.e., Passover/ Unleavened Bread for Israel, and Trumpets/ Atonement/ Tabernacles for Judah, respectively. This undoubtedly accounts in part for the odd fact that, for Jews, New Year's Day comes on 1 Tishri, the first day of the seventh Jewish month (in the fall)!
In the ancient Old World, the New Year celebration was viewed as the birthday of the world. It was a day of coronation of divine and earthly kings, a day of victory over chaos, a day of renewal of covenant and the reenactment of the king's enthronement, and a day of temple dedication and record keeping. There is good evidence that King Benjamin's address in Mosiah 1-6 was delivered on just such a great feast day. As for the Lamanite soldiers serving their new Zoramite king Amalickiah, certain events may show the symbolic importance of this New Year celebration. Imagine the confusion caused when the Lamanites awoke on New Year's Day to find that king Amalickiah had been murdered on New Year's Eve (see Alma 51:34-52:1). Note too the parallel timing of Teancum's killing of Amalickiah's brother Ammoron in Alma 62:36-39. This was the day when the king should have ceremonially conquered death and been reenthroned! [Robert F. Smith and Stephen D. Ricks, "New Year's Celebrations," in Reexploring the Book of Mormon, pp. 209-210]
Geographical [Theory Map]: Alma 51:1-24 Amalickiah Invades the Land of Moroni (25th Year)
Geographical [Theory Map]: Alma 51:1-24 Amalickiah Invades the Land of Moroni (25th Year) Sorenson
Alma 51:25-27 [Amalickiah] Takes Many Cities (25th Year)
Alma 51:28--52:5 [Teancum] Meets Amalickiah (25th Year)
Alma 51:28--52:5 [Theory Map] Teancum Meets Amalickiah (25th Year) Sorenson