Exactly as Xiao Xiao guessed, the undead's strength that were summoned depended on the casting time. Due to Shi Xiaobai's taunting, The Arch-Cardinal had choose not to hold back for a bigger and more powerful move. Instead, he would immediately summon the undead once a wave of skeleton soldiers was destroyed.
By considering the Arch-Cardinal's actions, be it taking the risk to forcibly intrude into this world or lose his calm and composure from Shi Xiaobai's taunting, it was easy to tell that the Arch-Cardinal had a high opinion of himself but had an easily enraged heart made out of glass.
Xiao Xiao keenly sensed this point and planned to use it to buy time.
Although her imagination was perfect, reality was cruel. Despite possessing a heart of glass, the Arch-Cardinal did not have a brain made of tofu. He could not have become an Arch-Cardinal in the Church of Virtuality if he was that stupid.