This verse is used as a time baseline for Book of Mormon dates. As such it is sufficiently accurate. To use it as an accurate measure of the precise time of the departure from Jerusalem and the birth of Christ perhaps stretches its function too much. As a round number, it is immediately suspect as a generality rather than a specific. As a rough yardstick it serves. As an accurate determiner, it likely will not.
The essential information in this verse is not the date (although the date is more important for modern readers, as it is information to which we would otherwise not have ready access) but the birth of the Messiah.
Translation analysis: The use of the title "Christ" in this verse, as well as other places in the text is perhaps indicative of at least one of the processes involved in the translation of the plates. "Christ" is the anglicized version of a Greek word, which was the substitution in meaning for the Hebrew word which we have in English as "Messiah", both meaning the anointed one. Clearly the concept of the person we know as "Christ" would have been present on the plates, but the specific word "Christ" would not have been. That our text contains "Christ" and not "anointed one" is an indication that Joseph Smith understood what the text of the plates meant and translated that meaning rather than slavishly translate only words. Thus Christ is an appropriate translation of the meaning, but might not be the best literal translation of whatever word actually existed on the plates themselves.