Just like the sacred days of the year mark the rhythms of the Jewish calendar, the daily prayers keep the beat of the clock. Shacharis, the morning prayers, ideally coincide with sunrise. Authorities debate whether Minchah should preferably mark early or late afternoon, but certainly not morning or night. Likewise, Ma’ariv is for evening and the first half of the night. R. Chaim Volozhiner (Nefesh Ha-Chaim 3b:4) compares praying after its proper time to blowing shofar on Pesach. It demonstrates a confused Jewish rhythm.
How you define these times–afternoon, evening and night–are among the first debates of the Talmud. Equally important is the question what to do when you have a competing priority. For example, authorities agree that you must pray Minchah by sheki’ah but they disagree over whether sheki’ah means sunset or dusk.1 Non-Chassidic Ashkenazic authorities tend to follow the former view. But what do you do if you cannot find a minyan before sunset? Does prayer in its time take precedence over prayer with a minyan, particularly when authorities debate whether the proper time extends later?
This is a very common situation. Many shuls schedule Minchah right before sunset. If people are only a few minutes late, you face this dilemma. On Fridays, when houses are often hectic preparing for Shabbos, the question becomes greater. There is a mitzvah to extend Shabbos. Praying Minchah after sunset means that you fail to extend Shabbos at all into Friday.2 Should you pray without a minyan before sunset?
The Mishnah Berurah (233:14) rules unequivocally that, any day of the week, you should pray alone at the undisputed proper time rather than wait for a minyan. At an urgent time, he allows prayer after sunset. However, if you have a choice between individual prayer before sunset and prayer afterward with a minyan, he rules you should pray earlier. However, others disagree and note that even according to the strict view, the period of time immediately after sunset (bein ha-shemashos) is doubtful day, doubtful night. Perhaps, they suggest, even the strict opinion would prefer you pray Minchah with a minyan during this doubtful period.
R. Shlomo Aviner (Commentary to Kitzur Shulchan Arukh, vol. 2 p. 339) quotes the Noda Bi-Yehudah (Orach Chaim 1:3) and Peri Yitzchak (2) as ruling that prayer with a minyan supercedes prayer at the proper time. R. Ovadiah Yosef (Yechaveh Da’as 5:22) permits waiting for a minyan within 13-1/2 seasonal minutes after sunset. R. Aviner also quotes R. Yitzchak Arieli (Einayim La-Mishpat, Berakhos 27a) as preferring prayer with a minyan after sunset over individual prayer before.
R. Eliezer Melamed (Peninei Halakhah, Tefillah 24:4) writes that most authorities rule that you should prefer to pray with a minyan after sunset over praying individually before. In a footnote (5), R. Melamed states that most leading Lithuanian rabbis followed the Mishnah Berurah, preferring prayer before sunset. However, most others ruled leniently. Among them is Sho’el U-Meshiv (3:247) and, more contemporary, Shevet Ha-Levi (vol. 9 no. 48).
Conclusion: ask your rabbi. My rabbi told me that he asked R. Dovid Feinstein who told him that we should wait for a minyan for six minutes after sunset, after which time we should pray individually. I’m not sure where the six minutes comes from. Perhaps he allows three minutes for the actual prayer, which brings you to nine minutes. His father, R. Moshe Feinstein, famously allowed women to perform a bedikah up to nine minutes after sunset (Iggeros Moshe, Orach Chaim 4:62).