Of most interest in these two verses is the combination of having traveled for three days, and then creating an altar of stones on which to offer a thanks offering.
The three days first tells us that they were only a certain distance south of Jerusalem. They were far enough away that it was unlikely that anyone would bother looking for them, but close enough that it would be possible for the two return trips that the sons took to Jerusalem (for the plates of brass and Ishmael’s family).
The three days is also of interest because a Dead Sea Scrolls text declares that sacrifices should not be made within a three days’ journey from the temple in Jerusalem. In Lehi’s day, there was a continuing process of centralization of worship in the physical location of the Jerusalem temple. It was a process that would eventually prohibit other temples.
However, during Lehi’s day, it appears that there was the ability to sacrifice when far from the Jerusalem temple. In fact, an Israelite temple has been discovered in Elephantine, Egypt that dates near this period. Thus, both sacrifices could be performed, and even another temple built, if they were far enough away from the Jerusalem temple. The absolute prohibition came later in history.
Lehi built an altar of stones. It is possible that Nephi intentionally phrased the construction of the altar in just this way. It is possible that Nephi is referencing Exodus 20:25, where Moses is told to make an altar of stone. Nephi will insert other references to Israel’s Exodus into his story of his family’s Exodus. The story of the building of the altar is not here for historical reasons, but for literary reasons that will tie Lehi and his family in the wilderness to the story of Moses leading the children of Israel through the wilderness to a land of promise.