Is it permissible to recite Surat Al-Mulk at any time, or must it be recited at night?

It is from the Sunnah (definition) to recite Surat Al-Mulk every night, as the Prophet, peace and blessings be upon him, would not sleep until he had recited it. It was narrated from Ibn Mas'ud that it prevents the torment of the grave, and from Ibn Abbas that it saves from the torment of the grave. A Muslim should be diligent in observing its recitation because it is one of the causes of salvation from the torment of the grave. The recitation of the Qur'an is permissible at any time unless the reciter is in a state of major ritual impurity (junub). Designating certain surahs for specific times is for recommendation, not obligation.