Minyan Versus Zman Tefila-Is it more important to Daven with a Minyan or to Daven within Zman Tefila?
Davening within the time period that the Sages established is more important than Davening with a Minyan. Thus, if one is Davening with a Minyan who will not reach Shemoneh Esrei before the conclusion of the Zman Tefila, it is better that he Daven in private in the Shul, rather than delay until after Zman Tefila to Daven together with the Minyan. He is not required to walk out of Shul to Daven Shemoneh Esrei.
Is it better to Daven Mincha in private before sunset than to Daven with a Minyan after sunset?
It is disputed amongst Rishonim and Poskim as to whether the time of Mincha ends with sunset or Tzeis Hakochavim. Practically, some Poskim it is better to Daven Mincha in private before sunset than with a Minyan after sunset. Other Poskim however rule it is better to Daven Mincha with a Minyan after sunset, then to Daven in private beforehand. It is unclear from Admur as to what his opinion is on the matter.
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 Admur 91:11; Michaber 90:10; Tur 620 in name of Rosh; Talmidei Rabbeinu Yona on Brachos 28b; Kol Bo 11; M”B 46:32
 Admur ibid; M”A 90:21 based on implication of Talmidei Rabbeinu Yona ibid; Elya Raba 90:11; Implication of Beis Yosef 90; Levush 90; Shisilei Zeisim 90:32; Kaf Hachaim 90:73
Other opinions: Some Poskim rule that if there is time available, he is to walk out of Shul in order to Daven Shemoneh Esrei, and not Daven in the Shul before the Minyan. [Bach 90, brought in M”A ibid; Olas Tamid 90:11; M”B 90:36]
 See Michaber 233:1 and Poskim there
 M”B 233/14
 Mor Uketzia 233; Shoel Umeishiv Giumel 247; Shearim Hametzuyanim Behalacha 69:1; Or Letziyon 1:20; Shevet Halevi 9:48; Eiynayim Lamishpat Brachos 27a; Piskeiy Tehsuvos 233:6
 Admur does not make clear as to what is defined as a time of need to allow delaying Mincha until after sunset. See Admur 90:11 that Davening within the Zeman is more important than Davening with a Minyan.