Based on no specific evidence whatever, but just as a working hypothesis, I wonder if a story that took many hours to tell over a number of days were at a fixed point in the day at the commission of some important person. It all depends on context, which I'm not aware of, but I can imagine some lord and his court having a story told in instalments over several days at a fixed point in the day, so it's an event everyone looks forward to, another way of a VIP being entertained while showing power and prestige. Since all the records were made by the literate, i.e. clergy and court, this would fit the general facts. I can't imagine this serialisation is something a modern performer can recreate, except at a week-long festival (I'm supposing a weekend festival wouldn't do it).