Ancient Hebrew Calendar

If I accept Professor Rachel Elior's claims that the Israelites followed a different calendar than the one used, as written in the Book of Enoch (she claims that this is the calendar The priests of the House of Zadok used it when they led the people, and the Hasmoneans abolished the calendar and changed it according to the Seleucids) if the rabbi knows the claims. If this is true, is this supposed to affect our lives today? It is possible that we do not fast Yom Kippur, but the holidays will remain as they should be? The claim that you will read them on their due date, even if you are a Jew, cannot hold true for keeping Shabbat on the wrong day.