Theophylact of Ohrid

The darkness was not in one place, but over all the earth. And if at that time it had been the period of the waning of the moon, then someone might still say that this was a natural eclipse. But now it was the fourteenth day of the month, when a natural eclipse is impossible.

Commentary on Mark ↗

Augustine of Hippo

What else, then, is the meaning of the evangelist Mark saying, "And it was the third hour, and they crucified Him," but this, that the Lord was crucified at the third hour by the tongues of the Jews, at the sixth hour by the hands of the soldiers? …

Tractates On John 117.1 ↗

Bede

And when the sixth hour had come, there was darkness over the whole land until the ninth hour. The most brilliant light of the world withdrew its rays, lest it see the Lord hanging, or the impious blasphemers enjoy its light. And it is to be noted, that the Lord was crucified at the sixth hour, that is, when the sun was about to withdraw from the center of the world; but at dawn, that is, when the sun was rising, He celebrated the mysteries of His resurrection. …

On the Gospel of Mark ↗