Q) Is one allowed to daven Ma’ariv before night on Erev Shabbos?
A) We previously quoted the Shulchan Aruch[1] who brings two views regarding the deadline for davening Mincha: according to the Rabbonon the time limit is nightfall, and according to Rebbi Yehuda the time limit is plag hamincha (i.e. 1¼ variable hours before nightfall).
The Shulchan Aruch rules that either of these two opinions are completely acceptable to follow – but one must be consistent and always follow the same opinion. This means that one can choose to daven Mincha after plag hamincha (until nightfall) – but then one must only daven Ma’ariv after nightfall (in line with the view of Rabbonon). Or, alternatively one can choose to daven Ma’ariv from plag hamincha – but needs to ensure to daven Mincha before plag hamincha (in line with the view of Rebbi Yehuda).
Regarding Erev Shabbos the Beis Yosef[2] and Mishna Berura[3] tell us that even those individuals who are careful only to daven Ma’ariv after nightfall during the week may daven Ma’ariv before nightfall after plag hamincha on Erev Shabbos, because there is a mitzvah of tosefes Shabbos (adding some additional time from the weekday to the actual time of Shabbos).
The Mishna Berura continues that one who wishes to daven Ma’ariv before nightfall should ensure to daven Mincha before plag hamincha. The Mishna Berura then quotes an opinion that maintains that a tzibbur may daven Ma’ariv before nightfall – even if they have davened Mincha after plag hamincha. The Mishna Berura concludes that one should not rely on this opinion unless there are extenuating circumstances and one is davening Ma’ariv during bein hashmoshos (i.e. after shki’ah).
[1] או”ח רל”ג א’
[2] או”ח ס’ רס”ז
[3] רס”ז ס”ק ג’