The Magen Avraham(494-1) asks, How can we say on Shavouos “Yom Matan Toraseinu”?
We pasken like R.Yosi that Matan Torah was on the 7th of Sivan. (not on 6th)
All poskim (Rambam ,Tur ,Shulchan Aruch etc.) say that on Shavouos we say ZMAN
Matan-and not YOM Matan- , so what’s pshat in the Magen Avraham's question?