Vatican II happened for a reason, that being lukewarmness in Faith. "Catholics" (nearly a billion of them) didn't really know and/or practice the Catholic Faith. If they had Vatican II could not have happened. There would have been revolt. Unfortunately there was not a revolt and by Divine Providence, a greater good will occur from this evil than if this chastisement did not occur.
My opinion on Vatican II. And we know how incorrect opinions can be.
"but for the sake of the elect those days shall be shortened." If Vatican II was prevented by God, then the lukewarm Faith may have degraded and changed after a long period of time. No one would perceive the changes, therefore no resistance, until no true Faith at all would remain. But because the days were shortened (Vatican II allowed accelerated change over a period of a few decades) some souls (elect) would recognize the evil, embrace the true Faith, and save their souls