Historical information: These two verses give us some idea of the dating of the text we are reading. Our current text for 1 Nephi and 2 Nephi was not begun until thirty years after the departure of the family from Jerusalem. The large plate tradition had been begun earlier (though also most likely after their arrival in the New World - unless a perishable version was begun in the journey from Jerusalem to Bountiful -they would not have appreciated the weight of yet another set of plates, not to mention the inability to find appropriate materials for them).
The next piece of information for dating the plates comes for verse 34 below. At that point, it is forty years after the departure from Jerusalem. Therefore, the entire text of the Book of Nephi this far was begun no earlier that thirty years after their departure, and this text is being written before forty years had passed. Therefore, Nephi began writing his second version of the history of his people after 567 BC, and finishes the end of this chapter by 557 BC. While there is a fair amount of text to this point, it is abundantly clear that it is not ten years of constant labor. This lets us know that the process of writing this second set of plates was accomplished over time, and that very little of the text is contemporaneous to the events described. While Nephi's other set of plates may have had some contemporaneous accounts (perhaps including Lehi's final blessings) there is no clear indication of that. The earliest material concerning the departure from Jerusalem likewise might have been part of the large plates, but it is equally as likely that each constituted a personal remembrance by Nephi, as he was a participant in each.