Albert Barnes Commentary Judges 7:19

"So Gideon, and the hundred men that were with him, came unto the outermost part of the camp in the beginning of the middle watch, when they had but newly set the watch: and they blew the trumpets, and brake in pieces the pitchers that were in their hands." — Judges 7:19 (ASV)

The middle watch - The old Jewish division of the night was three watches of four hours each. They are alluded to in Exodus 14:24; 1 Samuel 11:11; Psalms 63:6; Psalms 90:4; Psalms 119:148; Psalms 130:6; Lamentations 2:19. After the Jews fell under the power of the Romans, they used the Roman division of four watches of three hours each (Matthew 14:25; Mark 13:35).

“The beginning” of the watch would be about eleven o’clock at night.