Question: By the time I get home in the Winter, it is already after shekia. Is it better to daven mincha by myself before shekia or to daven after shekia in a chassidishe shul after shekia?
Answer: The Mishna (Berachos 26a) brings a machlokes as to whether one can daven mincha up until plag hamincha or until the evening. While Rashi and others define evening as nightfall, Rabbeinu Yona (Berachos 18b) and Rambam (Tefilla 3:4) hold that one only has until shekia as it corresponds to the korban tamid which mustn’t be offered after shekia. The Gemara writes that as this machlokes was never resolved, one can choose one time over the other (See Shibolei Haleket 48; Raavad 194). The Mishna Berura (Shaar Hatziun 233:18) writes that the machlokes as to whether we consider shekia or tzeis hakochavim the beginning of the evening is based on a machlokes between Rabbeinu Tam and the Vilna Gaon (OC 459:2) as to how we calculate shekia.
The Rosh (Berachos 4:3) and Shulchan Aruch (OC 233:1) write that one must choose one opinion and be consistent with it, not changing from one day to the next. Different communities have adopted different practices. Ashkenaz shuls typically daven mincha before shekia while chassidishe shuls are more inclined to daven after shekia (See Minchas Yitzchak 4:53:22).
There is a machlokes as to what one who usually davens earlier should do if they can’t get to a minyan until after shekia.
R’ Yaakov Emden (Mor Uketzia 233) and R’ Ovadia Yosef (Yechave Daas 5:22) write that it is preferable to wait to daven. R’ Shmuel Wosner (Shevet Halevi 9:48) writes that they should daven alone unless it has just turned shekia, in which case he should daven with a minyan.
Nonetheless, the Mishna Berura (233:14) writes that it is better to daven (and complete) mincha without a minyan before shekia than to daven later with a minyan. Only under extenuating circumstances, can one daven after shekia (Shaar Hatziyun 233:21). Similarly, many acharonim including the Aruch Hashulchan (OC 233:9) and R’ Moshe Feinstein (Igros Moshe OC 1:24) stress the importance of davening mincha before shekia.In conclusion, unless the minyan starts right before or at shekia it would seem preferable to daven by oneself rather than to daven with a minyan after shekia.