I think it is very telling that we do not have an exact date for the departure of Jesus at the end of 3 Nephi. It is almost as if there is no temporal end to his presence. He is still with these people in spirit and maybe even in close proximity physically. The book of 3 Nephi begins with a day, month, and year. We know exactly when the sign of his birth was given, but we do not know of any of the other such precise dates after the coming of Christ. It is almost as if time becomes irrelevant as 3 Nephi unfolds.
This is very uncharacteristic of most historical books, and also of the rest of the Book of Mormon. But something happens in the Holy of Holies. Anciently, it was seen as a timeless place and as a place of eternal perfection. The Holy of Holies was 10 cubits by 10 cubits by 10 cubits, a perfect cube, in which all things stood still, symbolizing the unity, the oneness, the eternal harmony of being in the presence of God. There, time becomes immaterial. From there emanates constantly the beginning and the renewal of creation. When the sacred order moves out into the next room in the temple, we find the days of the creation being represented. But in the Holy of Holies, in the presence of God, we are brought into a timeless context. Perhaps that is why we are not given the time or the day of the departure of Jesus. For indeed, he is still with us.
Book of Mormon Central, “Why Is So Little Said about the Timing of Christ’s Temple Ministry? (3 Nephi 10:18),” KnoWhy 481 (November 1, 2018).