When night fell in the Void Palace, it just made the blacks blacker. It was already difficult to see ahead of you in the day, but the darkness of night made it impossible to even see your hand before your face.
This wasn't normally a problem during the modern day because the Void Elders had set up formations that allowed a perpetual dull light. Though it didn't help with the fog, it made the transition from night to day almost impossible to track.
However, in a Zone like this one, back before the humans had reclaimed their territory, there was no such luxury. But, that also left things in the perfect state for Leonel and Aina. It made them even more difficult to detect in the darkness.