If a couple is married before sunset/shkiya on Sunday, and have sheva berachos on the following shabbos, do they have sheva berachos at shabbos shalosh seudos if they start before sunset/shkiya yet finish afterwards? ...Assuming we make a sheva berachos on shabbos at the third meal, but CYLOR when practical.
Sha'arei Teshuvah, Orach Chaim 188:8 quotes Ginat V'radim who writes that in such a case, even according to those who say we always follow the beginning of a meal, that only applies to mentioning the day's properties as part of birkat hamazon (i.e. in this case reciting r'tzei), but not to reciting sheva brachot.
Rav Ovadia (Yabia Omer (vol. 5 Even HaEzer 8), Yalkut Yosef (Sova Semachot 3:17, 17:12-17)) and Rav Moshe HaLevi (Birkat Hashem (vol. 4 page 395)) make heavy use of Safek Berachot LeHakel to avoid making Sheva Berachot beyond the seventh day. As such, if the last day of Sheva Berachot is Shabbat and Seudah Shelishit goes past the end of Shabbat, he argues not to make Sheva Berachot, against the Shevet HaLevi (vol. 1 Siman 39). However, he does permit making them during Bein HaShemashot, and if the meal finished after Bein HaShemashot, to still open with SheHaSimcha Bimono. Rav Ya’akov Kamenetsky is also quoted to be lenient with Sheva Berachot during Bein HaShemashot (Emet LeYa’akov, Kamenetsky, Even HaEzer 62 fn. 29), but Shemirat Shabbat KeHilcheta (59:18) and Rav Yosef Shalom Elyashiv (Mishnat HaGrys page 69) are stringent to not permit Sheva Berachot during Bein HaShemashot.