The epistles to the Corinthians are a direct account of those Corinthians keeping the sabbath, and the appointed times. Ditto for every other congregation that Paul visited in his journeys.
There is nothing in the entire NT to indicate that any gentile or hebrew christian did anything but keep the appointed times. As for the sabbath, Paul didn’t instruct them that they ‘must’ honor any day, but that we are placed at liberty, under our personal convictions under Christ.
The point is that there was either honoring the Lord’s sabbath, or not honoring it. There never was any other day to honor. “Sunday” worship came centuries later, instituted by a pagan dictator, interested solely in consolidating his personal power.
Read the epistles openly, without preconceived bias, and you will see what they were doing. Prayer helps too.
“The epistles to the Corinthians are a direct account of those Corinthians keeping the sabbath, and the appointed times”
The Epistle doesn’t say anything about the Corinthians keeping the Sabbath. Where do you think you see this in the Epistle?
which pagan dictator are you talking about and what was the reaction from the Christians when he did this?