Someone who was being yotzei Shalosh Seudas with mezonos may eat into the night (Shevet HaLevi Chelek 8 Siman 36). However what about when he makes “an al hamichiyah”? Is it just like bentching that he should also mention Shabbos even when it’s already night time?
Because the “seudah” is continuing from Shabbos, it appears that Shabbos should be mentioned in al ha-michyah, just like benching.
Note that the Shevet Ha-Levi refers only to somebody who is eating mezonos to fulfill his obligation of Se’udah Shlishis, so that the halachah will not apply to somebody who has already fulfilled his obligation.