After finishing with the record of Limhi, Mosiah reads (or has read) the account of Alma. Since we have much of these records in abridged form, the oral reading of the information would have take longer than it takes us to read the same information. Nevertheless, it is not surprising either that the entire account was read, or that the people would stay to listen to it. As was noted above, this was an occasion for new information, and would be the equivalent of a blockbuster mini-series for the Zarahemlaites.
What we are not told is how long it took to finish the reading. While the text does not explicitly say so, it would not be surprising if this were an event that took place over at least two days. Perhaps one day was devoted to Limhi and the second to Alma. What we have here is Mormon's abridging of the event, and Mormon is characteristically short on such details.