So Gideon, and the hundred men who were with him, came to 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 broke in pieces the pitchers that were in their hands.
"In the beginning of the middle watch"  (Judges 7:19).  Ancient Israel divided the night into three watches of four hours each - 6 o'clock to 10 o'clock, etc.  Therefore, the beginning of the middle watch would have been about 10:00 p.m., shortly after the changing of the guard.  By far the greater portion of the Midianite host would have been sound asleep.