Theophylact of Ohrid

But let us also consider what is said from another perspective. Evening signifies the end when someone dies in old age; midnight, when someone reaches the middle of life; cockcrow, when reason begins to unfold in us, for the cock signifies reason, which awakens us from the sleep of unconsciousness, and therefore, when a youth begins to exercise reason and to understand, then the cock, as it were, crows in him. Finally, morning signifies the very earliest age of childhood. Thus, all must think about the end of life. …

Commentary on Mark ↗

Gregory the Dialogist

Not only, however, those of us who rule over Churches, but all are required to watch the doors of their hearts, lest the evil suggestions of the devil enter into them, and lest our Lord find us sleeping. Wherefore concluding this parable He adds, Watch ye therefore: for ye know not when the master of the house cometh, at even, or at midnight, or at cockcrow, or in the morning: lest coming suddenly he find you sleeping.

Catena Aurea by Aquinas ↗

Bede

Therefore, keep watch; for you do not know when the Lord will come, in the evening, or at midnight, or at the cock's crow, or in the morning. Lest, when he comes suddenly, he finds you sleeping. However, the man who went on a journey and left his house, without a doubt, is Christ, who, ascending victoriously to the Father after the resurrection, left the Church corporally, which he nevertheless never deprived of the divine presence's protection, remaining in it all days until the consummation of the age. …

On the Gospel of Mark ↗