You know, just as a matter of historical curiosity, it’s quite unlikely the earliest Christians even used a seven-day week. The Jews did for religious purposes, having picked it up in Babylon during the exile in the sixth century, but the Greeks, Romans, and Egyptians — dominant cultures of the Mediterranean at the time — did not use seven-day weeks.
The Romans switched over during the reign of Constantine, possibly as a result of Christian pressure, but nobody really knows.
In any case, none of the Epistles contain any instructions for gentiles to observe any particular length of week, so it’s highly unlikely that the earliest Christians cared very much about which named day was observed religiously as the Sabbath.
Some archeological evidence suggests that at least in Syria and Egypt, Jewish and early Christian congregations sometimes shared facilities. If that practice was widespread, then it would make sense that Christians would gather on days that the Jews were not using the facilities, rather precluding a strict Christian observance of The Jewish Sabbath.
All of which goes to say that sometimes our traditions are less meaningful than we think they are.