סימן סט סעיף ב
עִקַּר זְמַנָּהּ הוּא בְּתֵשַׁע שָׁעוֹת וּמֶחֱצָה וּלְמַעְלָה, וְהִיא נִקְרֵאת מִנְחָה קְטַנָּה. וּבִשְׁעַת הַדְּחַק, כְּגוֹן שֶׁהוּא צָרִיךְ לָצֵאת לַדֶּרֶךְ אוֹ שֶׁהוּא צָרִיךְ לֶאֱכוֹל. יָכוֹל לְהִתְפַּלֵּל מִיָּד לְאַחַר שֵׁשׁ שָׁעוֹת וּמֶחֱצָה, וְהִיא נִקְרֵאת מִנְחָה גְּדוֹלָה. וְהֶמְשֵׁךְ זְמַנָּה הוּא לְכַתְּחִלָּה עַד שָׁעָה וּרְבִיעִית שָׁעָה קֹדֶם הַלַּיְלָה וְלֹא יוֹתֵר, וְזֶה נִקְרָא פְּלַג הַמִּנְחָה, כִּי מִשְּׁעַת מִנְחָה קְטַנָּה עַד הַלַּיְלָה הוּא שְׁתֵּי שָׁעוֹת וּמֶחֱצָה, וְהַחֲצִי מִזֶה הִיא שָׁעָה וּרְבִיעִית. ובְדֵיעֲבַד אוֹ בִּשְׁעַת הַדְּחָק, יָכוֹל לְהִתְפַּלֵּל עַד צֵאת הַכּוֹכָבִים. וְכֵן נוֹהֲגִין עַתָּה בְּרֹב הַקְּהִלוֹת, שֶׁמִּתְפַּלְּלִין מִנְחָה סָמוּךְ לַלָּיְלָה. וְשָׁעוֹת אֵלּוּ הֵמָּה שָׁעוֹת זְמַנִּיּוֹת, דְּהַיְנוּ לְפִי עֵרֶךְ הַיּוֹם, מִזְּרִיחַת הַחַמָּה עַד שְׁקִיעָתָהּ מִתְחַלֵּק הַיּוֹם לִשְׁנֵים עָשָׂר חֲלָקִים, וְאִם הַיּוֹם גָּדוֹל שְׁמֹנֶה עֶשְׂרֵה שָׁעוֹת, אֲזַי שָׁעָה וּמֶחֱצָה נֶחְשֶׁבֶת לְשָׁעָה.
The most proper time for the Minchah prayer is from nine and one half hours and on; and that is called Minchah ketanah.2Minchah ketanah, (minor Minchah). This corresponds to the afternoon tamid sacrifice which is the culmination of all the daily Temple sacrifices. When the situation is urgent, for example, if you must depart on a trip or if you must eat, you may pray [Minchah] immediately after six and one-half hours and this is called Minchah gedolah.3Minchah gedolah (major Minchah). This, too, corresponds to the afternoon tamid sacrifice. Six and one-half hours is the absolute earliest time that the afternoon tamid can be sacrificed. The time [for Minchah] is preferably, until one and one quarter hours before nightfall and not later. This (the 1–1/4 hours before night) is called pelag haminchah (lit. half of the Minchah), because from the time of Minchah ketanah until nightfall two and one-half hours elapse; half of this is one hour and one quarter. After the fact (i.e. this preferable time has lapsed) or in time of great need, you may pray until the stars appear. This has now become the custom in most congregations—to pray Minchah shortly before nightfall.4The Rabbanan and R. Yehudah disagree as to the times of Minchah and Maariv. The Rabbanan hold that the time for Minchah lasts until nightfall, when the time for Maariv begins. R. Yehudah holds that Minchah is until pelag haminchah (1–1/4 hours before nightfall) after which the time for Maariv begins. The Gemara concludes that both rulings are valid and one may choose either opinion.
Thus, if you pray Minchah before pelag haminchah, you may pray Maariv after pelag even before nightfall (remembering, of course, to repeat the Shema sometime after nightfall). Many poskim state that if you pray Minchah after pelag, you must wait until nightfall to pray Maariv. 5Mishnah Berurah writes that it is better to pray Minchah alone before sunset rather than to pray after sunset even with a minyan. In extreme circumstances, however, it is permitted to pray Minchah until a quarter of an hour before the stars appear. (Mishnah Berurah 233: 14) These [above-mentioned] "hours" are "time-variable hours," measured according to the length of daylight from sunrise until sunset,6Other Poskim hold that it is reckoned from day break until sunset. (Mishnah Berurah 233: 4) the day is divided into twelve parts. [For example] if daylight is eighteen hours then 1–1/2 hours is considered one "hour."
תנא דבי אליהו כל השונה הלכות בכל יום מובטח לו שהוא בן העולם הבא שנאמר הליכות עולם לו אל תקרי הליכות אלא הלכות (נדה ע"ג.)