"As I said before, I'm not here to fight. I just want to take something that belongs to me." Xu Shan wasn't in a hurry to reveal all his cards.
Even though he was in the same realm as the Divine Empress, there was no certainty how the battle was going to go, especially since she possessed the Book of Devouring.
Xu Shan didn't even know what that book was actually capable of, other than Devouring another person's strength. He wasn't in any hurry, especially since he had the initiative in his hands.
Now that things had actually come to this point, the only option was to become as strong as he could, before actually finishing the matters. There was still time before the Formation was completed by the Queen.
Fighting before that point was useless since he needed her to complete the formation.