CAN I READ PEREK SHIRA AND SHIR HASHIRIM AT NIGHT BEFORE MIDNIGHT?
With regard to the study of verse at night (especially before midnight), some permit the practice, whereas others, in particular those authorities who heed kabbalistic sources, are more stringent. This stringency would apply to Shir Hashirim, but Perek Shira might be permitted according to all opinions, because even though it is based on verses, it is a part of the Oral Tradition.
Sources; Kabbalists write that the night, and in particular the time of night between nightfall and chatzos, is not a suitable time for study of the Written Torah (verses of Scripture), which includes the recitation of Tehillim and Shir Hashirim. See Chaim Sha’al 2:25; Kaf Hachaim 228, and many other sources, all based on Arizal. It is unclear whether or not Arizal intended this prohibition to apply through to nightfall, or only until chatzos, but the common custom is to recite Tehillim after chatzos (see Yabia Omer, vol. 6, no. 30:6), though the study of verses other than Tehillim — included Shir Hashirim — is reserved for the actual time of day.
Although Mishnah Berurah (Shaar Hatzion 238:1) cites a dispute over the study of Scripture at night, he writes that there is certainly no prohibition in doing so, but only that it is better to study other parts of the Torah (the Oral Law) at night. This implies that wherever there is any need, it would be proper to recite Tehillim, and even to read Shir Hashirim, at night.
Concerning Perek Shirah, Osri Lagefen writes that it should only be recited after midnight, but Gam Ani Odecha cites an answer of Rav Chaim Kanievsky who writes that it stands to reason that its recitation is permitted even before midnight.