In some congregations, it was customary to pray Minchah and Ma’ariv, one right after the other, between plag haminchah and tzeit hakochavim. During the time of the Rishonim, this custom was practiced primarily in Ashkenaz, and in the time of the Acharonim, mainly in Spain. Many prominent rabbis questioned this minhag and attempted to abolish it, for it is a custom which contradicts itself; since they prayed Minchah after plag haminchah like the opinion of the Chachamim, it is impossible to pray Ma’ariv at that time like Rabbi Yehudah. Hence, it is proper to arrange Torah learning between Minchah and Ma’ariv, and in that way, the people praying will merit to learn Torah and to fulfill the Ma’ariv prayer in its proper time.
Nonetheless, the Acharonim instruct that if waiting until after tzeit hakochavim will cause the people to disperse and the Ma’ariv prayer to be cancelled, it is possible to be lenient and recite Ma’ariv immediately after Minchah. Of course, all those praying must repeat Keriat Shema after tzeit hakochavim.
Concerning an individual who normally prays according to the Chachamim’s approach, namely, Ma’ariv after tzeit hakochavim, and finds himself in a place in which they observe the minhag of extenuating circumstances – Minchah and Ma’ariv one right after the other before tzeit hakochavim – there is disagreement. Some say that it is preferable that the individual prays with them, so that he prays in a minyan. Others say that it is better that he preserves his minhag, prays Minchah with them in the minyan, but prays Ma’ariv individually after tzeit hakochavim.
. The Tosafot Berachot 2a, Rosh, and Talmidei Rabbeinu Yonah, as well as other Rishonim, question this minhag of praying Ma’ariv before sunset, for it involves two lenient opinions which contradict each other. In practice, to accommodate the needs of the multitude, they ruled leniently, as written in the Mishnah Berurah 233:11, Kaf Hachaim 12, and Yalkut Yosef, part 3, 235:1. However, all agree that Keriat Shema must be recited after tzeit hakochavim. There are two main opinions concerning the proper conduct in a place where the congregation is praying Ma’ariv before tzeit hakochavim. There are two main opinions concerning how one must practice when in a place in which the congregation is praying Ma’ariv before tzeit hakochavim. According to the Rambam, he recites Birkot Keriat Shema with them and adjoins redemption to prayer, and after tzeit hakochavim he goes back and recites Keriat Shema in order to fulfill the mitzvah. That is how the Shulchan Aruch 235:1 rules. According to Rav Hai Gaon, he only recites Keriat Shema with the congregation so that from Shema he will begin the Amidah together with the minyan. However, Birkot Keriat Shema, as well as Keriat Shema itself (in which he will fulfill his obligation), are recited after tzeit hakochavim. From his opinion it appears that it is better to recite Birkot Keriat Shema with Keriat Shema, after tzeit hakochavim, even though in so doing one does not adjoin redemption to prayer. This is what the Mishnah Berurah 235:12 writes and that is how he himself practiced (see Igrot Moshe Orach Chaim 2:60). According to the Gra, it is always preferable to pray Ma’ariv individually after tzeit hakochavim like the Chachamim rather than to pray with the congregation before tzeit hakochavim like Rabbi Yehudah.
In a place in which Minchah and Ma’ariv are prayed one right after the other, it is better, if possible, to be careful to recite Minchah before sunset and Ma’ariv after sunset, for some poskim maintain that Ma’ariv time begins at sunset, and that is how the Or L’Tzion, part 2, 15:6, understands the opinion of the Shulchan Aruch. Even according to this opinion, the time of Keriat Shema is after tzeit hakochavim. Nonetheless, the majority of poskim rule that the time of the Ma’ariv prayer according to the Chachamim is, indeed, after tzeit hakochavim. That is what the Mishnah Berurah 233:9 writes.
. The first opinion is inferred from Kaf HaChaim 233:12. One makes up the three paragraphs of Shema later. The second opinion can be inferred from Sha’ar HaTzion 235:16. However, if one prayed Minchah before plag haminchah he prays Ma’ariv with the minyan and follows one of the two opinions mentioned in the previous note.