There are various synonyms for the phrase "during the hours of darkness." Some of the most common include "at night," "in the nighttime," "after dark," "after nightfall," and "while it's dark outside." These expressions are all used to describe the time of day when the sun has set and ambient light levels have diminished, typically lasting from late evening until early morning. Other possible synonyms for this phrase might include "in the wee hours," "in the dead of night," "in the middle of the night," and "overnight." Whatever your preference, there are many ways to describe the period of time when the world is cloaked in darkness.