1) Could you please go through the times one can Daven Mincha and Ma’ariv- both earliest and latest for each. 2) Also, I believe that the problem lies when one wants to Daven both Mincha and Ma’ariv after Plag (before Shekiya). 3) So that Mincha is before Plag and Ma’ariv exactly at Shekiya, is this OK? If not do you have to wait until Tzet Hakochavim for Ma’ariv? Or how long after Shekiya?

1)The earliest time for Mincha: one half hour after midday, also called Mincha Gedolah. The latest time: disputed – Some contend sunset Some contend nightfall. The earliest time for Ma'ariv: Some contend at Plag Hamincha, which is 43/48 of the day. According to those who calculate this on the basis of sunrise and sunset (the most common accepted approach) this is 1 and a quarter of a Halachic hour before sunset. Others contend that the earliest time for Ma'ariv is sunset. Still others contend that the earliest time for Ma'ariv is nightfall. 2) This is correct; because one is creating a contradiction. 3) According to almost all opinions. Certainly follows traditional practice.