The phrase “First Day of the Week” should not be found in new testament. It is not in the Greek. In the Greek text what is found is “mia ton Sabbaton”, “First of Sabbaths”. Here is Matthew 28:1 with Strong’s numbers.
“In the end(G1161 G3796) of the sabbath(G4521), as it began to dawn(G2020 G5723) toward(G1519) the first(G3391) day of the week(G4521)“
Notice the Strong’s number G4521 after the words Sabbath and week. G4521 is the Greek word Sabbaton. So the verse should read as follows:
“Now after the Sabbath, as it began to dawn on the first of Sabbaths, Mary Magdalene and the other Mary came to see the tomb.”
First of Sabbaths is a specific Sabbath in the Spring of the year. Note that every time you see the phrase “first day of the week” in your translation it was or was about to be Spring. Sabbath is also hidden behind the word rest in Hebrews 4:9.