The time of night with regard to reciting Tehillim begins from tzeit hakochavim (the emergence of the stars), and not from sunset.
Sources and Explanations
In the sefer Mei Yehudah (siman 22, cited in Yabia Omer vol. 6, ot 6) he writes that night, with regard to reciting Tehillim, begins from the time of tzeit hakochavim, just as we find that the Taz (131:8) permits saying Tachanun (the supplication prayer) during bein hashemashot (twilight), for as long as it is not definitely night, that is, tzeit hakochavim, one may say Tachanun. If so, the same applies with regard to saying Tehillim.
From the sefer “Shaf Veyativ – Laws of Saying Tehillim” by Rabbi Shay Tahan, Chapter 2: The Proper Times for Saying Tehillim, Halacha 9 (p. 21 in the print edition). Translated from the Hebrew original.
