Ok, I might just be totally wrong, but my gut is telling me that the date here is significant.
Many in these last days/end times extremist groups are trying to decipher the time periods of things in scripture, and for LDS people this is more than just the Bible. This involves the astronomy above (signs in the stars and sky), as well as the Hebrew calendar, and trying to be watchful of the various prophecies occurring. I have a mild personal interest, but it only goes so far. There is some significance to the time period that these kids vanished. I think this falls in the area of Rosh Hashanah (sp?) which is the Day of Atonement and I think the start of a new year in regards to the Jewish faith (anyone Jewish or more familiar please feel free to correct me).
In the LDS literature sept 23rd is significant as it marks a period of time with Joseph Smith Jr. that has to do with the fulfillment of some sort of prophecy. Right now it's all hitting a wall of a headache in my head, but maybe with this info someone can dig deeper into that date. It might all be coincidence, and it might not, but with these extreme prepper end times types, this kind of topic is very important to them. I hate to say what someone else has already said, that there very well may be an answer to this buried in his books. He wrote them as "fiction" because he didn't want the criticism, but he claimed to personal friends that much of this was based on what he believed was visions and NDE's he personally had.