Real day for Sabbath not named in the Bible

In the Book of Genesis chapter 1, mentioning God’s creation days as ‘first day, second day’, and of course ‘seventh day’ in Genesis chapter 2, however, these days were not named like Monday as the first day and Saturday as the seventh day.
If the Bible did not name the days, then obviously someone else apart from the Creator named these days to suit his or her own requirements.
For example, if one was to choose Tuesday as Sabbath day, then his first day would be Wednesday and so on.

Anointed Christian