فَاسْتَهْوَانَا السَّمَرُ إِلَى أَنْ غَرَبَ الْقَمَرُ وَغَلَبَ السَّهَرُ
Our night conversation absorbed us until the moon set and wakefulness prevailed.
Gharaba al-qamar / ghalaba al-sahar place two short verb–subject units side by side. The moon sets and wakefulness dominates, showing the gathering's talk extending deep into the night.
The patterned clauses have narrative work to do: they measure the passing of time. It is also crucial to distinguish samar, night conversation, from sahar, wakefulness. Sonic resemblance and chronological progression reinforce one another.