When dawn came, the activities of the zombies were no doubt being lessened to a certain degree. Half Ghoul Lord Derek could only deduce that why the zombies were more active in the night based on his experience and his fellow zombies under his command is that they were somewhat affected by the solar energy of the sun.
"It might have something to do with the celestial's powers. Perhaps, under the power of the sun, we become more indolent so that it would be easier for the Celestials to control us if they want to?" Derek was not able to give a concrete answer to Yinn and her team when the squad asked him such a question.