Revelation 1:9-10, “I, Yoḥanan, both your brother and co-sharer in pressure, and in the reign and endurance of יהושע Messiah, came to be on the island that is called Patmos for the Word of יהוה and for the witness of יהושע Messiah. I came to be in the Spirit on the Day of יהוה,a and I heard behind me a loud voice, as of a trumpet.”
Malachi 4:1-6, "4:1, "“For look, the day shall come, burning like a furnace, and all the proud, and every wrongdoer shall be stubble. And the day that shall come shall burn them up,” said יהוה of hosts, “which leaves to them neither root nor branch."4:2, "“But to you who fear My Name the Sun of Righteousness shall arise with healing in His wings. And you shall go out and leap for joy like calves from the stall."4:3, "“And you shall trample the wrongdoers, for they shall be ashes under the soles of your feet on the day that I do this,” said יהוה of hosts."4:4, "“Remember the Torah of Mosheh, My servant, which I commanded him in Ḥorĕḇ for all Yisra’yl – laws and right-rulings."4:5, "“See, I am sending you Ěliyah the prophet before the coming of the great and awesome day of יהוה., "“And he shall turn the hearts of the fathers to the children, and the hearts of the children to their fathers, lest I come and strike the earth with utter destruction.”
Both the Day of YHWH, so am I missing something you are saying? I don't see anything about Sunday here.