John Cassian, The Institutes II.17: How he who rouses them for prayer ought to call them at the usual time

But he who has been entrusted with the office of summoning the religious assembly and with the care of the service should not presume to rouse the brethren for their daily vigils irregularly, as he pleases, or as he may wake up in the night, or as the accident of his own sleep or sleeplessness may incline him. But, although daily habit may constrain him to wake at the usual hour, yet by often and anxiously ascertaining by the course of the stars the right hour for service, he should summon them to the office of prayer, lest he be found careless in one of two ways: either if, overcome with sleep, he lets the proper hour of the night go by, or if, wanting to go to bed and impatient for his sleep, he anticipates it, and so may be thought to have secured is own repose instead of attending to the spiritual office and the rest of all the others.