During the summer months, Shabbat starts late, which can be difficult for families with younger children, who tend to either fall asleep before their father comes home from shul or be tired during the entire meal. Therefore, many people accept Shabbat early. Where does this custom come from and under which conditions may Shabbat be accepted early?
R’ Yehuda and the chachamim differ (Tractate Brachot 4:1) as to when zeman tefillat mincha (the time period for daveningmincha) ends. According to the chachamim, mincha can be said until the evening (i.e. shekiah – sunset), but R’ Yehuda opines that zeman tefillat mincha ends at plag hamincha (one and a quarter sha’ot zemaniot before shekiah).
R’ Eliezer ben R’ Yoel HaLevi (Brachot 1) explains that the chachamim did not specify a specific start time for maariv, because the end of zeman mincha coincides with the start of zeman aravit.
The Gemara (BT Brachot 27a) concludes that since the Mishna did not rule in favor of either position:
“One who does as [one] master – does [correctly], and one who does as [the other] master – does [correctly].”
In other words, one can follow either the chachamim or R’ Yehuda. However, both the Shulchan Aruch and the Rama (Orach Chayim 233) imply that one must be consistent. But other authorities feel that one may follow the chachamim one day and R’ Yehuda on another.
The Shulchan Aruch (263:4) rules that the candles must be lit after plag hamincha, because before plag hamincha, it would not be clear that the candles are being lit in honor of Shabbat.
Several practical guidelines:
At the “early” minyan on Fridays, mincha must be concluded before plag hamincha, and kabbalat Shabbat should not begin until after plag hamincha. Accordingly, mincha should be scheduled for 15 minutes before plag hamincha. However, in many locations, the “early” minyan is held at the same time each week, and this latter practice does have a halachic basis. (See Rav Uri Samet’s article in Techumin 26 for further details.)
The candles must not be lit before plag hamincha.
One who accepts Shabbat early may not perform melacha once s/he has accepted Shabbat.
Ideally, one should make Kiddush half an hour before shekiah and eat a kezayit pat (a measurement of food) after tzait hakochavim (nightfall).
One must repeat all three paragraphs of the Kriat Shema after tzait hakochavim.
For hilchot nidah, the count is based on shekiah, even for women who accepted Shabbat earlier.
In locations where every shul accepts Shabbat early, the entire community must accept Shabbat early.