R' A&C Walters asked:
> There is a similar halocho brought down beshaim the Gr"o,
> that davening maariv bezaman (after tzais) without a minyan
> is better than davening earlier (from Plag) with a minyan,
> even on shabbos. Does anyone know what his mekor for this is,
> befrat the Gemoro says "Ravi Tzali shabbos beerev shabbos"

I once heard the following argument, but unfortunately I have no 
sources for it inside. Namely: According to other poskim, Birchos 
Krias Shema have the same zmanim as Shmoneh Esreh, but according to 
the Gr"a, Birchos Krias Shema have the same zmanim as Krias Shema 
itself.

According to this, other poskim allow us to say Shema early in the 
morning, and then say all of Shacharis in the hour between Sof Zman 
Shema and Sof Zman Tefila. But according to the Gr'a, there is 
nothing gained by saying Shema early, and the latest one might delay 
shacharis is to reach Ga'al Yisrael in the last moment before Sof 
Zman Shema, and then continue with Shmoneh Esreh.

Getting back to R' Walters' question, if the above is accurate, then 
saying Brichos Krias Shema of Maariv prior to nighttime would be 
Brachos Levatolos, and it would be better to daven later without a 
minyan than to say brachos levatolos witht he early minyan. And when 
the Gemara says that Rav davened maariv on Erev Shabbos at Plag, 
perhaps the Gr"a would say that this means that he said the Maariv 
*Amidah* of Shabbos at Plag, but he said Shma (and Birchos Shma) 
later on, at night.

HOWEVER I must admit that if the above is accurate, then it is NOT 
TRUE that the Gra would say that it is better to daven a late maariv 
without a minyan than an early maariv with a minyan. Rather, he would 
say to daven Shmoneh Esreh with the early minyan, and to say Shma and 
Brachos later -- just like the case of where one walks into shul to 
find them ready to start the Maariv Shmoneh Esreh.

Akiva Miller