2. The conclusion of the blessing beginning with the word "Hashkiveinu" in
the evening service on Shabbos, differs from its conclusion during the week
of "Shomer amo Yisroel" ("Who protects His people Israel"). During the
week, this blessing is a request for protection on behalf of the Jewish
people as a whole. However, on Shabbos, the Jewish nation doesn't need to
be guarded, since the Shabbos itself protects us.
Therefore, after requesting, "Spread over us the shelter of Your peace," we
omit the references to undesirable influences, and conclude: "Blessed are
You, G-d, who spreads over us..." This rule also applies on a festival.
[The following rules apply] should one err and conclude in the manner one
does during the week: If one remembered directly after reciting the [final]
word [of the blessing] - "lo'ad" - one should say, "haporeis sukkas sholom"
("Spread out your shelter of peace") immediately. If, however, one did not
remember until after pausing slightly (1), one need not say anything more.
(1) If one waited longer than the time it takes to say the words, "Sholom