There are records among the Jews to defend their 7th day as the Sabbath - And as the day that Yeshua recognized (having made no correction), and the day that HE attended Synagogue, I have naught to do but follow him.
Virtually everyone knows WHEN the Sabbath is, even though they don't keep it.
I don’t have a problem with the 7th day. But how do you know that Saturday is the 7th day that they reference?