It is interesting that Alma declares that he does not know how soon the Savior will come, since the scriptures had predicted a rather direct number of years, and the countdown will prove that prophecy to have been accurate. As with all of us who live in the present, it is often difficult to understand when the scriptures are literal and when they are figurative. Alma knew of the 600 year prophecy of Lehi, just as surely as he had read Nephi's writings about the Nephites as the wanderers and scattered, and the plainness of the scriptures. While he must have read the prophecy, he must not have been able to discern whether that was specific or generic. Even, however, had he known the year, he would not have known the day. Alma had to wait with faith, as do we all.