On the second day; either the day after his first laying of the siege, or after the taking of Makkedah and Libnah.
Related Commentaries of Joshua 10:32
Joshua 10:32
32 And the LORD delivered Lachish into the hand of Israel, which took it on the second day, and smote it with the edge of the sword, and all the souls that were therein, according to all that he had done to Libnah.