One of the most important figures of that time had been Ri'neref, who wrote the Age of Earth. While the main population of Ronay migrated to Terahnee, Ri'neref had persuaded a smaller portion of the Ronay to follow him to D'ni. According to the DRC, the king of the Ronay at the time also allowed other small groups to splinter off from the bulk of the people leaving for Terahnee, but the exact number of other groups and their total size relative to the rest of the population is unknown.
The exact timeframe of the exodus is also not known, but conservatively, it would have lasted from 59 BE (when the imminent destruction of the world became public knowledge), until at least 0 DE when the last settlers relocated to D'ni. However, the exodus could potentially have taken much longer on the Terahnee side, as the bulk of the Ronay migrated to that Age.