The Bible Dictionary passage on ‘Lord’s Day’ say “The first day of the week is meant, being the day of our Lord’s Resurrection and also the day on which the Holy Spirit came upon the Apostles . . . . It was never confounded with the Sabbath, but carefully distinguished from it.”

So, as you can see, “Sabbath Day Observance” is, in and of itself, an incorrect term. It should be “Lord’s Day Observance.” The reason that the word ‘Sabbath’ has persisted in our culture is because all of the scriptures in the Old Testament that say ‘Sabbath’ are principles with promises, and not tied specifically to Saturday, but to “the day of rest” in general.

Maybe it is semantics, but the literal Sabbath is Friday at sundown until Saturday at sundown, and the Lord’s Day is commemorated in the Church as 00:00 early Sunday morning until 23:59 Sunday night, except for some regional circumstances that Gramps pointed out.

That being said, there is the letter of the law and the spirit of the law. We shouldn’t think “How late can I stay out partying on Saturday night”, nor should we think “When is Sunday over so I can start partying.”