Translation:Shulchan Aruch/Orach Chaim/281

1. When one reaches the words “to You, we give thanks,” in [the prayer] Nishmas, he should not bow as one does in the blessing Modim, for one should bow only in those places where our Sages instructed that we do so. RAMA: Our custom is that on Shabbat we come a bit later to the synagogue than we usually do on the weekdays, because the tamid sacrifice of the weekdays was said in the morning and on Shabbos we say "and on the Sabbath day" later. (Mordechai). And it is customary to increase the hymns of praise recited on Shabbos, every place according to its custom. In any case, if one does not say them we do not go back except if one did not say 'לאל אשר שבת'; for this one does go back and say it. It is befitting to prolong the hymns of praise recited on Shabbos and recite them with a pleasant melody as an expression of honor for the day. One should not admonish a sheliach tzibbur who prolongs their recitation even though the intent of the one delivering the admonishment is to prevent the neglect of Torah study. (Or Zaruah). In all cases, on Shabbat and Yom Tov we do not prolong their recitation too much, so we may eat prior to the sixth hour, as above in Siman 288.