Wondering if biphasic sleep was involved with those schedules -- but it is not obvious to us now?
https://en.wikipedia.org/wiki/Biphasic_and_polyphasic_sleep#...
"Historian A. Roger Ekirch has argued that before the Industrial Revolution, interrupted sleep was dominant in Western civilization. He draws evidence from documents from the ancient, medieval, and modern world. Other historians, such as Craig Koslofsky, have endorsed Ekirch's analysis. According to Ekirch's argument, adults typically slept in two distinct phases, bridged by an intervening period of wakefulness of approximately one hour. This time was used to pray and reflect, and to interpret dreams, which were more vivid at that hour than upon waking in the morning. This was also a favorite time for scholars and poets to write uninterrupted, whereas still others visited neighbors, engaged in sexual activity, or committed petty crime. The human circadian rhythm regulates the human sleep-wake cycle of wakefulness during the day and sleep at night. Ekirch suggests that it is due to the modern use of electric lighting that most modern humans do not practice interrupted sleep, which is a concern for some writers. Superimposed on this basic rhythm is a secondary one of light sleep in the early afternoon."