Chemish makes an extremely short entry. Chemish indicates that he saw his brother's last entry. This is at least suggestive that Amaron was on his deathbed when writing. It is tempting to link his death with the events he has just described. The event of the destruction was certainly impressive, and Amaron gives us virtually no indication of how the community was restructured after the loss of a significant part of their population. These omissions are at least suggestive that Amaron was wounded in the war, and eventually died of his wounds, passing the records to his brother Chemish.
Textual: I would suggest that Chemish writes his brief account in two sittings. The first comes very soon after receiving the plates. He describes the way he receives them, and his words appear to be an opening statement for the record. The phrase "and after this manner we keep the records" would appear to belong with the charge to keep the plates. Rather than mention "genealogy" as did Jarom and Omni, he simply notes the charge that the plates be kept.
Since the paragraph is essentially introductory, I suggest that Chemish wrote it soon after receiving the plates with the intent to write more later. However, he clearly had nothing to say, and at some later point when he was ready to pass the plates on, he simply ended his entry and gave the plates to his son. Of course there is no indication of how long he kept them, but we may suppose that they were not in his possession for a large number of years, as he was of the same generation as Amaron who had the plates for 38 years. Chemish would be expected to have been at least that old when he received the plates, and perhaps older (though clearly a younger brother to Amaron, as it would have been the right of the firstborn to receive the plates).