It is the custom in many communities to bring in Shabbos earlier during the summer months when the days are very long.  Since it is possible to daven ma’ariv after the “plag haminchah” which begins an hour and a quarter before sunset according to many authorities, then “kabbales Shabbos” is valid and once that takes place all of the laws of Shabbos are valid and its laws are all applicable.  

In the Shulchan Aruch Orach Chaim, 263, 12 it is stated: - If the majority of the community have already davened “kabbales Shabbos” then the minority are bound to follow and observe Shabbos which has been accepted by the majority.  In commenting on this statement the Mishnah Berura writes that if the majority of the city or town were not yet in shul then anyone arriving there would not be compelled to observe Shabbos in following the minority and the same would apply in a place where there are several synagogues, then each one is considered as a separate entity that it is not required to abide by the “kabboles Shabbos” of another shul even if it has a majority of worshippers.

 I reference to the above R. Moshe Feinstein, O.B.M. (Igros Moshe Orach Chaim III, 38) discusses the situation of the husband who has gone to shul and accepted Shabbos early, his wife after that time of “kabboles Shabbos”is also bound to observe this early Shabbos since there is a general rule that the wife is required to follow the minhag of the husband.  However he states a distinction in regard to this principle.  The wife is only bound to the husband’s “kabboles Shabbos” if that kabbole was done only with the sincere intent to bring in the Shabbos earlier in order to reap the benefit of an extended “kdushas Shabbos.”  

However since it is a known fact that the earlier minyanim were established only in the summer months for the convenience of having the meals at an earlier time then this situation does not establish a type of minhag that would compel the wife to accept the earlier time assumed by her husband and consequently she may for herself still do certain aspects of work without any restraints.