Shabbat Shalom, James,
As I was looking through some miscellaneous scraps of paper this morning, I came across a note that may be of interest to you. Distinguished from all other days, the seventh day, when God ceased from all His work which He had done/made, is the only one which does not begin with evening followed by morning (Gen. 2:1-3).
From God’s perspective (if I may reverently so say), the Sabbath brings to an end His work creatively and prophetically, and divides time between the kingdoms of this world and the Kingdom of God/Heaven which is not of this world/cosmos/aeon (John 18:36), between that which is flesh from that which is spirit (John 3:5-7): it is a transition day. even as the millenial kingdom will be , dividing time from eternity, when time is no more, symbolized now by the ‘one’, the ‘eighth’ eternal day going outside the repetitive cyclical passage of a week of days. Jesus, whose birth and life ,death and burial fulfilled the Sabbath even as He fulfills all the other appointed times and feasts of the LORD, carried on the redemptive work of the Father (John 5:15-47) to both restore and to reconcile all things to God.
What is interesting regarding the distinctive reckoning of the Sabbath without the normal evening/morning is that during the crucifixion of the Author of Life, from about the 6th hour (12 noon) until the 9th hour (3:00 p.m.), there was extraordinary, supernaturally imposed darkness over all the Earth (and I believe throughout the creation), bringing to an end the rule of the kingdom of darkness, the blood of Jesus Christ accomplishing full redemption of things in the heavens, on the earth, and under the earth unto God to whom it all rightfully belongs (Luke 23:44-46). That darkness represents the death of all mankind through the death of Christ, who bore our sin and punishment. No one can enter the Sabbath rest of God except he be born again by the Spirit from above through repentance and faith in the gospel of God concerning Jesus Christ and the Kingdom of God, both confessing and believing from the heart that Jesus is LORD and that God has raised Him from the dead.
Ultimately, as the Lord informed His disciples just before His ascension to the right hand of the power of God, times and seasons have been reserved by the Father in His own authority. Our only certainty of salvation and part in the first resurrection is abiding faith in the Lord, our God and Savior, and in His Word. Praise God for whatever things He chooses to make known to us, and thank God, too, that the simplest and feeblest-minded can come to Him through the simplicity that is in Christ.
Whether any of this has any bearing on your thinking through the created calendar and its relevance I leave with you. In any case, your research and findings have afforded me opportunities to consider these matters in a new and fresh manner, for which I express my appreciation.