When the Greek is translated as originally intended in Matthew 26:17 and Mark 14:12 using the dative of reference, the text in both scriptures reads “with reference to the” first day. Matthew and Mark were not saying they were currently “on the” 14th day.
One day in 2002, I was in church listening to a sermon when the pastor mentioned that Westcott and Hort’s literal translation (as seen in The Kingdom Interlinear Translation of the Greek Scriptures) is often much better at staying true to the meaning of the Greek articles and prepositions than many other translations…