John Chrysostom

"He saw in a vision, evidently," etc. It was not in his sleep that the Angel appeared to him, but while he was awake, in the daytime, "about the ninth hour. He saw an Angel of God coming in unto him, and saying unto him, Cornelius. And when he looked on him, he was afraid." So occupied was he with himself. Implying, that it was in consequence of the Angel's calling him by a voice that he saw him; as, had he not called him, he would not have seen him: so taken up was he with the act in which he was engaged.

Homily on Acts 22 ↗

Theophylact of Ohrid

"He in a vision clearly saw about the ninth hour of the day an Angel of God, who came in to him." He sees an Angel to supplement Peter's faith. Or, rather, not for him, but for others, weaker in faith. "About the ninth hour of the day," when he had set aside his cares and was in quietness and rest.

Commentary on Acts ↗

Bede

He clearly saw in a vision at about the ninth hour of the day, etc. He rightly receives the oracle to seek baptism at the ninth hour because in the death of Him, who surrendered His spirit at the ninth hour, he was to be baptized.

Commentary on Acts ↗