«فَلَمَّا لَاحَ ابْنُ ذَكَاءَ»
When the sun appeared.
Ibn Dhakāʾ is an uncommon literary expression for the sun. Rather than simply saying “morning came,” the narration gives daylight a memorable poetic name. Lāḥa means to appear or become visible.
The change of time also changes what the narrator can do: he can examine faces, locate the sound he heard, and resolve the mystery. Dawn advances the action, not merely the clock.