You may perhaps try read my book, 'The Lord's Day in the Covenant of Grace', find it here:
http://www.biblestudents.co.za. Click on 'Book 2, Resurrection'. With your 'search' button on your 'My Documents' menu, you can enter any of the terms used in this Scripture, and it will give you all the results through any of the books.
The expression is always used as a retrospective reference to PAST events. The time and the day on which reference is made to the day of the referenced event
naturally cannot be identical. It's like that in any language. We shall party after a rugby game won, until after twelve o'clock, and say, What a game have we had today! A year after we shall recall that game and say, What a party we had that day! The game actually was on the day before; the party actually was on the day after!
So the historic context determines which day is actually spoken of or referred to. The grammar does not literally determine the real facts; the style does. The matter is one of Stilistics, not of Grammar or Syntax. Nevertheless 'ekeinos' is a Demonstrative Pronoun, which explains any difficulties. It does not cancel out Grammatical sense.
So in John 20 Monday is the time of reference being made to the actual (previous) day of event.
Read much more said ... specifically.