The last recorded reference to time before the Nephite gathering was when Mormon recorded in Mormon 5:6 that "in the three hundred eightieth year the Lamanites did come again against us to battle, . . . and they did tread the people of the Nephites under their feet. And it came to pass that we did again take to flight, and those whose flight was swifter than the Lamanites did escape, and those whose flight did not exceed the Lamanites' were swept down and destroyed." How long it took after these battles began for the Nephites to begin gathering to Cumorah is not mentioned. It seems probable that the gathering, or plans to gather, started immediately with the flight of the Nephites in the year 380, especially in light of the hill Cumorah's apparent strategic military value. Whatever the case, Mormon records that "when three hundred and eighty and four years had passed away, we had gathered in all the remainder of our people unto the land of Cumorah" (Mormon 6:5). It is interesting to note that if the Nephite gathering took four years (which the chronological data supports), then this time period would be the exact time period that the Jaredites took to gather at the hill Ramah for their final battle (see Ether 15:14). [Alan C. Miner, Personal Notes]
One might ask, Why would the Lamanites allow a period of up to four years for the Nephites to get ready? According to John Sorenson's theory, in the first place, the Lamanites would understand from their knowledge of the regional geography that the Nephites had no place to retreat to beyond Cumorah, for behind them lay only the huge estuary of Alvarado (the Ripliancum of the Jaredites) and the tangle of rivers and swamps known in modern times as "La Mixtequilla." So both sides knew this would be a decisive battle between the ancient rivals. Another reason the Lamanites would be agreeable to this place and appointed time may have been that they needed a period to build up their own forces for the climactic clash, for they were a long distance from their home base. In any case, the agreed site was deeper into the now-limited territory under Nephite control so the Lamanites had nothing to lose. [John L. Sorenson, An Ancient American Setting for the Book of Mormon, p. 348]