תפילת ערבית מפלג המנחה

Under what circumstances can you pray Arbit from Plag HaMinchah?

Not including Shabbat - never.

Assuming you pray Mincha until sundown.

עבד כמר עבד means you choose one opinion and stick with it.

i recall the rabbi permitting it on friday, not true?

That’s what I meant when I said not including Shabbat (friday night).

Although the Rabbi himself never davened early.

thank you