For in six days the Lord made heaven and earth, the sea, and all that in them is, and rested the seventh day; wherefore the Lord blessed the Sabbath day, and hallowed it. Exodus 20:11
"Like the Sabbath, the week originated at creation, and it has been 
preserved and brought down to us through Bible history.
God himself measured off the first week as a sample for successive weeks to the close of time.
Like every other, it consisted of seven literal days. Six days were employed in the work of creation; upon the seventh, God rested, and he then blessed this day, and set it apart as a day of rest for man."
E.G.W.