As Scripture teaches that the Sabbath was enjoined upon all people at Creation (Gen. 2:2-4), as the moral, Fourth Commandment commands it (Ex. 20:8-11) and as the New Testament upholds keeping the weekly Sabbath on the first day of the week (Jn. 20:19; Acts 20:7-11; 1 Cor. 16:2; Heb. 4:9; etc.), so the question of when the Sabbath begins should be of concern to every person.
In the most comprehensive treatment to-date on the subject, Rev. Fentiman in this academic article demonstrates from Scripture that the Sabbath has always been from dawn-to-dawn since Creation throughout the Bible, without exception.
Fentiman, Travis – The Biblical Sabbath is from Dawn to Dawn 2018 97 pp.
To give a brief summary of the Biblical evidence:
The word ‘morning’ in the Creation account in Gen. 1 is more accurately translated as ‘dawn’, the phrase signifying that each day of Creation ended with dawn, with the next day beginning therefrom. The Old Testament speaks of days starting from the morning or dawn in over 30 verses. The Israelites kept the Sabbath morning to morning in Ex. 16 and the rest of Old Testament history is consistent with this reckoning.
The New Testament throughout its pages likewise reckons days to start in the morning. The Temple in the New Testament counted the hours of the day from 6 A.M. The disciples’ buying of spices in the evening after the death of Jesus is shown to be inconsistent with an evening-to-evening reckoning of the Sabbath. The Resurrection accounts of Christ rising from the dead at dawn assume continuity with the Old Testament reckoning. Christ celebrates the Lord’s Day in Jn. 20:19 with the disciples in the evening of the 1st day of the week, which the apostles continued to practice in Acts 20:7-11.
The corruption of the Sabbath by Jewish traditionalism in keeping the Sabbath from evening to evening likely started in the inter-Testamental era and was preserved in their Talmuds. A very full survey of the inter-Testamental and extra-Biblical literature is surveyed on the issue, as well as reformed history.
Assure your mind and heart on this Scriptural subject and make the Sabbath a delight! (Isa. 58:13-14)