פירוש על ברכות 3:12

Rashi says that we are not Yotzei Keri'as Shema in the Beis ha'Keneses during the day. We say it only to enter Shemoneh Esre amidst Divrei Torah. One is Yotzei Shema through the first paragraph during Keri'as Shema Al ha'Mitah. The Yerushalmi says so. The Riva, Ritz Gei'us and Rav Amram Gaon agreed. R. Tam says that we are Yotzei in the Beis ha'Keneses, we hold like R. Yehudah. The Gemara said that one who did like either opinion was fine. This is difficult. The Gemara said so about Tefilah, which corresponds to Korbanos. Minchah was never offered after Plag ha'Minchah! Rather, we hold like other Tana'im who hold that the time for Shema is before Tzeis ha'Kochavim. We are lenient like R. Yehudah regarding Tefilah because it would be hard to gather people again. L'Chatchilah, one should say Shema after Tzeis ha'Kochavim, like our Stam Mishnah. Rav Hai Gaon said that in Eretz Yisrael we pray Ma'ariv, and afterwards we say Shema in its time, even though we lose Semichus Ge'ulah l'Tefilah. However, he must pray Minchah before Plag ha'Minchah.

From nightfall - This is when the sun has completely set as we learn later on.