Originally Posted by David Mooney

This so-called "mid-week Sabbath" is an invention of those who want to escape the implications of a failed prpohecy by Jesus. There never was a mid-week Sabbath in the Spring of the Jewish Calendar until long after the Diaspora. The Christians first brought up the idea of the
mid-week Sabbath early in the second century A.D. with the Gospel
of Peter - source