Shulchan Arukh, Orach Chayim 267/שולחן ערוך·אורח חיים רס״ז

1 The Laws Pertaining to Prayer on Friday, 3 Seifim: Tachanun is not said during Minchah on Erev Shabbat.

2It is customary to recite the Evening Service earlier than on weekdays. During Plag HaMinchah one may light and accept Shabbat in Ma'ariv, and one may eat immediately. (See Siman 253 regarding how we measure the time for Plag HaMinchah).

3One should not conclude the blessing Hashkiveinu with the words Shomer amo Yisrael, “the Guardian of His people Israel,” [as he does during the week]. Instead, when he reaches the phrase uvetzeil kenafecha tastireinu (“shelter us under the shade of Your wings”), he should say “ufros aleinu sukkas…. Baruch Atah A-donai haporeis… (“spread over us the shelter…. Blessed are You, G‑d, Who spreads….”).