All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.
Being saved from the torment of the grave occurs for those who recite Surah Al-Mulk [Quran 67] alone, and the fact that there is a Hadith about the desirability of reciting Alif, Lam, Meem Sajdah [Quran 32] and Surah Al-Mulk does not prevent that it is Sunnah as well to recite Al-Mulk alone.
Therefore, whoever recites it without reciting Surah As-Sajdah has done a desirable act and it is hoped that he will be protected from the torment of the grave, Allah willing.
One gets the virtue of reciting it if he recites it at any part of the night, whether directly before bedtime or long before it. One also gets its virtue if he recites it in ‘Isha’ prayer or its Sunnah or at night optional prayer because he is considered as having recited it by night, although we have not come across an explicit statement of the scholars about it, but the grace of Allah is vast.
Allah knows best.