[Uri’el-2012]

“kyriakos hēmera, - the Lord’s day, not what has been erroneously translated as the Day of the Lord. A careful study of Revelation makes it clear that John did not want to get the two confused and besides, the phrase “Lord’s Day” was already in common use in the church by AD 90 as further indicated by the Didache (late 1st Century) and Justin.

Review the Septuagint,
YHvH is called L-rd in the Septuagint.

A Torah-observant Jew as was John
would be referring to YHvH as L-rd.

Thus the L-rd's day would be Shabbat
not the Pagan day of the sun.

shalom b'SHEM Yah'shua HaMashiach Adonai

[Godzilla]

Review the Septuagint, YHvH is called L-rd in the Septuagint. A Torah-observant Jew as was John would be referring to YHvH as L-rd. Thus the L-rd's day would be Shabbat not the Pagan day of the sun.

John was also a disciple of Jesus and a Christian, with all that involves, and the understanding that the law pointed towards Jesus as its fulfillment. I'm sorry if the use of Greek by John in Revelation - reflects the established usage in the NT is indicative of the First Day of the week. That the day of the week became known later as Sunday means little to a believer - because it is just a word. What makes it significant to Christians is that it is the day of the week Jesus Christ rose from the dead. And whether or not that day is named Sunday, mother goose or donaldday, the significance does not come from the name, but the event associated with the particular day of the week.

[Petronski]

Thus the Lord's day would be Shabbat
not the Pagan day of the sun.

Nope.

The Lord's day is Sunday,
not the Pagan day of saturn.