Saying Avadim Hayinu:
The custom in these provinces is that [after] Mincha of Shabbos Hagadol, we recite “Avadim Hayinu” [until Lichaper Al Kol Avonoseinu], as Shabbos Hagadol was the beginning of the redemption and the miracles. This applies even if Shabbos Hagadol falls on Erev Pesach.
 430/2; Rebbe in Haggadah Shel Pesach
Other Opinions: The Shaar Hakolel [48/1] writes that from the fact that Admur omitted this in his Siddur, it is evident that in his Siddur he holds that one does not say it on Shabbos Hagadol. So rules also Gra. It is likewise omitted from the Siddur of the Arizal. Nonetheless, the Rebbe writes in his commentary on the Haggadah that the custom is to say it, unlike the ruling of the Shaar Hakolel.
 Rebbe in his commentary on the Haggadah
Other Opinions: From Admur in his Shulchan Aruch ibid it is implied that Avadim Hayinu is to be said after the Chazzans repetition of the Amidah, as Admur states “In place of saying Barchi Nafshi (which is not said according to our Nusach) one says Avadim Hayinu” and Barchi Nafshi is said before Aleiynu. [see Siddur Yavetz]
 Rebbe in his commentary on the Haggadah.
Opinion of Admur: Admur in his Shulchan Aruch does not write until where one should read.