A point to consider with regard to the abbreviated sleep schedule of monks is the restive and restorative aspects of the meditative periods during each day. For Catholic and Orthodox monks the periods of centering, contemplative, and some other types of prayer are the same as or comparable to other meditation practices which have documented restorative value. From my experience the more time spent in meditation the less sleep needed. Even doing hard labor, digging ditches and building stone walls, during a meditation retreat provide enjoyable engagement that support the still times. Anecdotally, placement of prayer just before sleep facilitates a more rapid entry into both sleep and deep sleep.
