According to a secondary source (The Four Major Cults, German edition, by Dr. Anthony A. Hoekema), the noted NT scholar F.F. Bruce maintained that Luke used the Roman, not the Jewish time reckoning, i.e. a day was from midnight to midnight in Luke’s Gospel and the Acts of the Apostles. The primary source may be “Commentary on the Book of the Acts” [Grand Rapids: Eerdmans, 1955]. I did not take the time to chase it down.

I have found your quotation of Ignatius in his Letter to the Magnesians, Section 9, from approximately the year A.D. 107, as quoted by Lightfoot in the Apostolic Fathers. There is some question as to its original formulation, due to textual variants. This should not surprise us, for the copyists would not have been as exacting with regard to non-canonical writings as they were with the Scriptures themselves. If variants were common in copies of the sacred Scriptures, how much more likely must they be with regard to secular works?

I also found a quotation from the Didache “Teachings of the Twelve Apostles” from the late 1st or early 2nd century, section 5 (paragraph 14): “Now according to the Lord’s day, gather together and break bread and give thanks, after acknowledging your wanderings to one another, so your sacrifice would be a clean one.”

Then there is the reference to the “eighth day” from “The Epistle of Barnabas” (15:8-9). The letter itself was quoted as early as the second century by Clement of Alexandria. “Finally He saith to them; Your new moons and your Sabbaths I cannot away with. Ye see what is His meaning; it is not your present Sabbaths that are acceptable [unto Me], but the Sabbath which I have made, in the which, when I have set all things at rest, I will make the beginning of the eighth day which is the beginning of another world. Wherefore also we keep the eighth day for rejoicing, in the which also Jesus rose from the dead, and having been manifested ascended into the heavens.”

From the First Apology of Justin Martyr, chapter 67, written around A.D. 155, we read: “the Sunday is the day on which we all hold our normal assembly”. With regard to the Christians from the nations: “the heathen who believe on Him (Christ) … will receive the inheritance … although they neither ever observed the Sabbath, nor were circumcised, nor observed the feasts.” (Dialogue with Trypho, Chapter 26 of the Ante-Nicene Fathers, I, 207 – my translation from a German source)

I came across a website that had a brief, but interesting consideration of the issue: http://www.gci.org/law/sabbath/history3. The group GCI, founded by Herbert Armstrong, has some quirky ideas in their doctrinal statement. Nonetheless, their page about the Lord’s Day has interesting information with footnotes that may be useful for this consideration.

I would also add the following from my own personal study of the subject recently:

A. The sabbath (or rest) principle existed in terms of example since the creation week (Genesis 2).
1. God rested.
2. God blessed it. (1:22, 28; 2:3; 5:3)
3. God set it apart. (2:3; Exodus 13:2; 19:10, 14, 22-23; 20:8)
4. God did not call it “Sabbath” at this point, but “the seventh day.” (Genesis 2:3)
5. God did not regulate it, apparently, although He specifically regulated several other matters.
a) He regulated fruitfulness. (Genesis 1:28)
b) He regulated the dominion of man over creation. (same verse)
c) He regulated diet. (verse 29; 2:16-17)
d) He regulated marriage. (2:24)
e) He regulated further matters, including bloodshed. (9:1-7)
B. The sabbath precept had to be taught to the children of Israel. (Exodus 16 – certainly much had to be taught a nation that had spent so much time in heathen Egypt.)
1. Exodus 20:8 makes reference to “the sabbath day.” Its definiteness (“the”) indicates that it was already known to the children of Israel at this point.
2. It was in fact known to them, but not primarily because of the creation week, but rather because of another situation that was very fresh in their memory. (Exodus 16:5, 22-30)
a) They should receive twice as much bread from heaven on the sixth day (verse 5)
b) Yet they were surprised (verse 22)
c) It was “a sabbath” (verse 25), that is literally “a rest.” Translations with the definite article are few.
d) It became “the sabbath” (the rest) that God had given specifically to them, the children of Israel (verse 29).
C. The sabbath then became law (Exodus 20:8-11; Deuteronomy 5:12-15)
1. The holy remembrance of the “rest” prescribed in Exodus 20:8-11
a) How it was to be observed (verses 9-10)
b) Who was to observe it (verse 10 – Jews and also non-Jews who were living among the children of Israel)
c) Why it was to be observed (verse 11) – the example of the LORD. Young’s Literal Translation: “therefore hath Jehovah blessed the Sabbath-day, and doth sanctify it.” Note the two tenses.
2. The sanctity of the “rest” according to Deuteronomy 5:12-15
a) The specific application to the children of Israel: 21 second-person references in 4 verses. (Admittedly second-person references are not absent from the other nine commandments. Romans 2:14-15 indicates that the law was written on the hearts and present in the consciences of the Gentiles. Is sabbath observance intuitive for an unseared, but unregenerated conscience?)
b) The extent of the application to strangers: “within your gates” (verse 14)
c) The rationale behind the command: This time not, “the Lord rested,” or “the LORD brought [others] out,” but “the LORD brought you out … therefore the LORD commanded you to keep the sabbath day.” (verse 15)
3. A further confirmation of the specific Jewish application of this law: Jeremiah 17:22 – “sanctify the sabbath day, as I commanded your fathers.” Subsequent verses (through verse 27) apply the teaching to the southern kingdom.

Perhaps this straight-forward approach to the Scripture may help to shed light upon the development of the teaching in the Old Testament, even before the teaching of the New Testament is brought into the picture. (Please excuse my taking up so much space on your website.)

The reference in Acts 20:7 is interesting – in the Jewish culture the day begins at Sunset (because Genesis says God created the evening and the morning…), so as Jamie said, the events in this passage would undoubtedly have been on Saturday night. Jewish people mark the end of the sabbath with a short service called Havdallah (meaning separation) to mark the transition between the one special day and the six regular days, and I am told that in Biblical times the Havdallah ceremony involved the breaking of bread. This is also consistent with Paul speaking until midnight and planning to leave the next day (Sunday) – travel on the sabbath was restricted.

Rev 1:10 is a bit of a mystery to me (I’ll have to ask an expert) , but we shouldn’t let a single verse with uncertain meaning detract from a consistent view in the rest of the Bible.

Regarding the early church leaders, these were notoriously anti-semitic and wanted to rid the church of its Jewish character, so I wouldn’t give much weight to their views.