Lord’s Day in Revelation is not referring to a day to worship the King of Kings at all:

Revelation 1:9. I John, your brother and partner in affliction and in kingdom and in patient expectation in Y’shua, I was on the island called Patmos because of the Word of God and the testimony of Y’shua. 10. I was in the Spirit on the Lord’s Day and I heard behind me a loud voice like a trumpet 11. saying, “You must write in a scroll what you see and you must send it to the seven congregations, in Ephesus and in Smyrna and in Pergama and in Thyatira and in Sardis and in Philadelphia and in Laodicea.”