In the book of Acts, Christians began to gather on the first day of the week. I believe this is what the Revelation passage is speaking to. And none of this addresses the Sabbath which was fulfilled in Christ.
Act 20:7 And upon the first day of the week, when the disciples came together to break bread, Paul preached unto them, ready to depart on the morrow; and continued his speech until midnight.
Here in the MKJV it is stated correctly.
Act 20:7 And on the first of the sabbaths, the disciples having been assembled to break bread, being about to depart on the morrow, Paul reasoned to them. And he continued his speech until midnight.
This verse in Act 20:7 is speaking of the counting of the Feast of Weeks. Each Sabbath after the Passover, you count 7 Sabbaths until you reach 49 days (also known as counting the Omer). The 1st of THE SABBATHS IS Day 1 of counting the Omer.
The Feast of Weeks
Lev 23:15 And you shall count to you from the next day after the sabbath, from the day that you brought the sheaf of the wave offering; seven sabbaths shall be complete.
Lev 23:16 To the next day after the seventh sabbath you shall number fifty days. And you shall offer a new food offering to Jehovah.
The Christian proof text fails to hold up that is was the 1st day of the week (ie Sunday) when it was actually a Sabbath (ie Friday sundown to Saturday sundown). Paul preached into the Sunday, when he was free to travel because the Sabbath had passed.