The time of the Ma’ariv prayer was established to correspond to the offering of the organs and fats of the Tamid offering upon the altar. As we already learned (earlier in this book 24:7), the Chachamim and Rabbi Yehudah disagree regarding this matter. According to the Chachamim, the time of Minchah is until night, and the time to pray Ma’ariv starts from tzeit hakochavim. According to Rabbi Yehudah, the time of Minchah ends at plag haminchah, an hour and a quarter before the end of the day, and immediately after that begins the time of Ma’ariv. A person is permitted to choose whether to practice according to the Chachamim or Rabbi Yehudah, on condition that he adheres to one minhag. If he follows Rabbi Yehudah, he must make sure not to pray Minchah after plag haminchah. If he follows the Chachamim, he must make sure to pray Ma’ariv after tzeit hakochavim. However, if a person prays Minchah after plag haminchah in the opinion of the Chachamim, it is forbidden to pray Ma’ariv before tzeit hakochavim according to Rabbi Yehudah.
Even though according to Rabbi Yehudah the time to recite Ma’ariv and Birkot Keriat Shema starts at plag haminchah, the time of Keriat Shema itself does not begin until tzeit hakochavim. Therefore, a person praying before tzeit hakochavim must repeat the three paragraphs of Shema after tzeit hakochavim (Shulchan Aruch 235:1).
L’chatchilah, one may not switch from one ruling to another; instead, everyone must always practice according to one opinion. The prevalent minhag today is to follow the Chachamim. However, in times of need, a person is permitted to change from the Chachamim’s opinion and practice like Rabbi Yehudah. For instance, in the summer, when Shabbat starts late, there are those who wish to accept Shabbat early so that their small children can participate in the prayer service and the meal, and for that reason they pray Ma’ariv like Rabbi Yehudah, before sunset. Similarly, a person who finds himself in a place in which they practice like Rabbi Yehudah, even though he is used to praying Ma’ariv after tzeit hakochavim, it is better that he pray in a minyan like Rabbi Yehudah, instead of observing his minhag and praying individually like the Chachamim.
. However, the Tosafot write in Berachot 2a that according to Rabbeinu Tam, the time to recite the evening Keriat Shema is the same as the time of Ma’ariv, and according to Rabbi Yehudah, one is permitted to fulfill his obligation from the time of plag haminchah. According to Rabbeinu Yitzchak, it is permissible in extenuating circumstances to be lenient regarding the time of Keriat Shema and to follow the opinions which say that it is a few minutes before tzeit hakochavim. Nonetheless, the remaining Rishonim maintain that the time to recite the evening Keriat Shema is after tzeit hakochavim, and therefore it is necessary to repeat Keriat Shema after tzeit hakochavim, as the Shulchan Aruch 235:1 rules. There is disagreement as to whether it is necessary to repeat the Vayomer paragraph after tzeit hakochavim as well. According to the Magen Avraham, the time to remember the Exodus from Egypt is the same as the time of Ma’ariv and one need not make it up, whereas according to the Sha’agat Aryeh its time is like the time of Keriat Shema and one must make it up (Mishnah Berurah 235:11). Regarding Birkot Keriat Shema, in principal their time is like the time of Keriat Shema. However, in practice, those who follow Rabbi Yehudah normally recite them before tzeit hakochavim and fulfill their obligation, as clarified in the Mishnah Berurah 235:7 and 11, and Sha’ar HaTzion 6.