John Gill Commentary Judges 20:30

"And the children of Israel went up against the children of Benjamin on the third day, and set themselves in array against Gibeah, as at other times." — Judges 20:30 (ASV)

And the children of Israel went up against the children of
Benjamin on the third day
Not the day following the second battle, since it would take more time to go to Shiloh, and fast and offer sacrifices there, but on the third day from the second battle:

and put themselves in array against Gibeah, as at other times ;
as they had done on the first and second days of battle.