http://revach.net/article.php?id=2334

Section: Halacha   Category: Tshuvos
When Should You Daven Maariv?

The Shulchan Aruch (OC 235:3) says that L'Chatchila you should say Krias Shema at night immediately after Tzais HaKochavim.  This requires davening Maariv, in order to say Shema with the Brachos. The Mishna Brura brings from the Levush that the reason for this is because of Zerizim Makdimim L'Mitzvos.
 
The Piskei Tshuvos (235:9) lists a number of exceptions in the Poskim including if you are learning, if there is a minyan that you can Daven "B'Rov Am", or if you are "Oseik B'Tzarchei Tzibbur".  He himself says that if there is a later minyan nearby your home, you are not obligated to look for an earlier Minyan.  Nor should you say Krias Shema at the Zman without davening the complete Maariv.
 
The Piskei Tshuvos also brings the Aruch HaShulchan (235:18) who questions the psak of the Shulchan Aruch since based on the Rishonim (Rashba, Rosh, and Tur) there is no obligation to daven right after Tzais.  This in fact, says the Aruch HaShulchan may be the reason why most people are not Makpid to daven right after Tzais.
 
Important Note: We try to convey the Tshuva to the best of our ability. We admit that our understanding may not be accurate. Please also understand that this Tshuva may not be the final word on this topic. One should consult a Rav before drawing any conclusions.

This article has not been reviewed by the posek of the AskRevach section, Rav Peretz Moncharsh.  Any questions regarding this topic and Halacha L'Maaseh may be asked to him at www.revach.net/ask