Ten years ago, a Mormon FReeper had claimed that the term "Christian" came into use after the apostasy had occurred. That places the falling away as occurring during the Acts Of The Apostles (specifically prior to Acts 11:26), since that is where the Bible records Jesus' followers were "first called Christians". If that is true, then the apostasy began less than eight years after Christ's ascension, the LDS' Melchizidek Priesthood was stripped away from the Apostles themselves for the majority of their ministry, and most (if not all) of the New Testament, which was written by the Apostles, was written during their apostasy from Jesus Christ.
The Mormons I know disdain the teachings of the Apostle Paul, and many doubt that he was actually an Apostle since he never followed Jesus while Jesus was alive on earth, and that by the time Saul became Paul, the apostasy had already occured.