A Quranic Journal: Surah al-Muzzammil ayah 6

The point is that Nashi'ah of the night refers to its hours and its times, every hour of it is called Nashi'ah, so it refers to the periods of time. The purpose of this is that standing at night (for prayer) is better for training the heart and the tongue, and more conducive to recitation... [The night is] more comprehensive for the matter of performing the recitation and better for understanding it than in the recitation of the day. This is because the daytime is the time for people to disperse and move about, to raise voices and be lively