Alma 17:6

Now these were their journeyings, having taken leave of their father Mosiah, in the first year of the reign of the Judges; having refused the kingdom which their father was desirous to confer upon them; and also this was the minds of the people;

Here is how their journey started. They said goodbye to their father Mosiah in the first year of the judges. Their father wanted to give them the kingdom, but they said no. The people wanted this too.

Their mission began when they left their father Mosiah in the first year of the judges. They’d turned down the throne their father wanted to give them, and the people had agreed to let them go.