Neither Genesis 1-2 or Exodus 20:9-10 ever use or qualify the sabbath by the words "of the week" and for good reasons. Such a restriction would have denied God the right to apply the Sabbath rest to anyting other than a literal 24 hour day and/or to any other day than the seventh day "of the week." However, the Sabbath rest is applied to a seventh YEAR as well as a 50th year in addition to 24 hour days, as well as other days in the Jewish calander month other than the seventh day "of the week." It is applied to the 1st, 7th, 8th, 14th, 15th, 21st and 22nd of the days of the month in Leviticus 23. Hence, the Sabbath command is stated in language that is inclusive of these applications. In regard to days it is merely six days working followed by a Sabbath regardless of what particular day "of the week" that may or may not fall upon. The Jewish calander and all other human calanders and was a DATE rather than DAY orientated calander based upon a Luner month with additional days added throughout the year to make a full year. This is easily seen for the DATES given for SABBATHS in Leviticus 23. However, even the term "day" or "yom" in the proper context can exceed a 24 hour day as seen in its use in Genesis 2:4 which sums up the whole seven day period as one "day." Or in the context where "a day is as a thousand years and a thousand years as a day." Therefore even in the use of "day" in the fourth commandment there is grounds to apply the Sabbath principle to longer time spans than 24 hours but to a "month" or "year" or a "millenium" thousand year period. This broader principle is encapsulated in the fourth commandment wording that gives it ability to be applied far wider than a 24 hour Sabbath or to be restricted to any particular day of the week but applicable to any day of the week or month God chooses to apply the sabbath law (Lev. 23). Everyone of the ten commandments have an external application but they also have an inherent broader application and are inseparable from each other as to fail in "one point" is to fail all points - James 2:10. The fourth commandment is so worded to include both the external and inherent broader principle as evidenced by its broader application in Leviticus 23-25. Hence, the fourth commandment only requires one in seven days to be designated as Sabbath without any regard to what particular day that sabbath may or may not fall upon. The phrase "of the week" is purposely omitted to allow for the Jewish Calander for time zone differences and for a change of Sabbath under the New Covenant. That change is predicted in Psalm 118:20-24 with Acts 4:30-31 and Mark 16:9 and Hebrews 4:1-11 and Revelation 1:10.