BH Please explain Plag HaMinchah. How does one figure out what time is plag haminchah? Why is it important? What does it have to do with davening minchah / maariv during the weekday, and more importantly, what is it's importance in regard to davening on Friday afternoon & night - thank you.
Answer:
Pelag Haminchah is one and a quater sha'os zenanios (halachic hours) after minchah ketanah (or the midpoint between minchah ketanah and the end of the day). Minchah ketanah is nine and a half sha'os into the day.
It is important in that if one prays minchah before pelag, it is permitted to pray maariv after pelag (following the opinion of Rabbi Yehudah, who maintains that the time of minchah extends until pelag).
In addition, this is the time from which one is able to accept Shabbos. Before this time, it is not possible to accept the Shabbos, and only from this time can one cannot light candles or make kiddush.