How come the accounts of war in the Book of Mormon occur at the exact seasonal times we would expect?

If Joseph Smith had written the Book of Mormon himself, would he have taken time to work out the times of the year that wars would most likely occur?

John L. Sorenson notes how the Nephite year was arranged something like the following:

Field preparation and cultivation: months 4-9
Main harvest: months 10-12
Time of warfare: chiefly months 11-3

He then goes on to explain:

When we look carefully at what the Book of Mormon says about war, we find that the many military activities reported did not take place just anytime during the calendar year. Rather, they occurred according to a definite pattern. Certain months were war months while others were not. The complete consistency of this pattern reminds us of how many details the writers of this scripture kept straight.
Over all, we find remarkable consistency in the handling of these highly technical bits of war and calendars. Most of us would not have been alert enough in writing a book about wars to have kept all this straight in our heads. If Joseph Smith had simply made up a “golden Bible” on the basis of his own experience and the locality where he lived, as some critics believe, then the thirty-two battles at the end and start of the year in the Book of Mormon would have fallen in western New York’s windy, icy winter, a major error! The “heat” suffered by the Nephite and Lamanite soldiers and Amalickiah’s death on new year’s eve (Alma 51:33-52:1) would have been a hilarious blunder. Instead, the timing of wars we find in the scripture is part of a consistent pattern. It all agrees with what the Book of Mormon says about itself—that it is a translation from an authentic ancient American record.
– John L. Sorenson – Seasons of War, Seasons of Peace in the Book of Mormon

How did Joseph Smith manage to keep this in mind when dictating the Book of Mormon?

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