I was wondering how do we say Tehillim in Kriat Shema she’al Hamittah if we should not say Tehillim before midnight? Similarly, many have the custom of saying Tehillim while being Shomer a meit, even before midnight. What is the reason for these exceptions?
The Be’er Heitev 238, 2. brings the Arizal’s opinion that “Mikra” should not be said at night. In Sha’ar Hatziyun 238, 1. he quotes the Be’er Heitev and writes that in the Pri Megadim in sounds that one can read Mikra, and adds the Sha’ar Hatziyun, even according to the stringent opinion there is no prohibition here, it is only better Lechatchilah to learn Mikra during the day. This is derives from what it says in the Midrash that the Holy One Blessed be He was learning with Moshe Mikra during the day and Mishnah at night. Therefore according to the opinion of the greatest Posek of the last generations the Mishnah Berurah, it is permitted to read any Mikra including Tehilim at any time of the night also according to Kabala. Also among the Mekubalim who are stringent not to read Mikra at night, there is a variety of opinions. There are different opinions on what part of the night one should not read. There are those who say that the prohibition is only on Torah not on Nach so Tehilim is not included. Others say that the prohibition is only when read in a way of learning but in a way of prayer and pleading it is permitted. Some others say that Tehilim is not included altogether because it is songs and praises. See at length in Tzitz Eliezer vol. 8, 2.