In Mosiah 17:4 it is recorded that Alma "fled from before [the guards of Noah]." For Alma1, this event marked the beginning of an extensive sojourn in the wilderness. How long was Alma1 in the wilderness? The answer to this question is dependent upon four factors:
1) Alma's departure date from Lehi-Nephi was about the year 460* [ *From when Lehi left Jerusalem]
If Alma1 died at age 82 (Mosiah 29:45) in the year 510, then he was born in the year 428. If we assume that Alma was named a "priest of Noah" at 30 years of age (see Appendix A) and was 32 years old by the time Abinadi was tried, then adding 32 years to his birth year (year 428) gives us 460 as the year when Alma fled from the land of Lehi-Nephi.
2) Ammon's departure date from the land of Zarahemla was about the year 480.
If:
Mosiah2 begins to reign in the year 477 (Mosiah 6:4),
Benjamin lives 3 years and dies (which would make it the year 480) (Mosiah 6:5),
Mosiah2 has 3 years of peace (the same last 3 years of Benjamin's life--still the year 480) (Mosiah 7:1),
Mosiah2 sends Ammon at this time to the land of Nephi (Mosiah 7:2) and he wanders 40 days before he arrives (Mosiah 7:4);
Then: Ammon would have departed the land of Zarahemla in the year 480 and arrived that same year (40 days later) in the land of Lehi-Nephi.
Note* The first edition (1830) of the Book of Mormon has Ammon saying that "Benjamin" could translate the 24 gold plates (p. 200). This name was changed to "Mosiah" (Mosiah 21:28, 8:13-14) in later editions; however, the change brings up a chronological point. When Ammon left Zarahemla, was king Benjamin (although not necessarily the reigning king) still alive? Did Benjamin die before Ammon's return so that only Mosiah2 was there to welcome them (see Mosiah 24:25)? We know that by at least 30 years after Ammon's statement concerning the power of either Benjamin or Mosiah to translate ancient records, Mosiah2 had acquired those same powers because he translated the 24 gold plates (see Mosiah 28:11). It is possible that in order to avoid confusion for the reader, Joseph Smith made a change. That change, for whatever reason, has altered just slightly the perceived chronology of Ammon's departure. Nevertheless, according to the chronological timetable expressed thusfar (and in Appendix A), Ammon could have actually departed Zarahemla some weeks or months before Benjamin's death and satisfied either the term "Benjamin" or the term "Mosiah".
3) The arrival of Ammon, and Limhi in the land of Zarahemla was about the year 480.
Although nothing is said about the length of time that Ammon was with Limhi's group before their escape to Zarahemla, we will assume that it wasn't more than a few weeks. Mormon records that immediately after Ammon made his report to king Limhi, he and the king "began to consult with the people how they should deliver themselves out of bondage; and even they did cause that all the people should gather themselves together" (Mosiah 22:1). It wouldn't have taken long to develop a plan, but the preparations for the escape and rapid emigration would require a few days to a few weeks because whole families would be traveling with their flocks and herds (Mosiah 22:8). Travel time was termed "many days" (Mosiah 22:13); however, it would have been at the most not much more than 40 days because they were not only in flight but they apparently knew their way. Thus it probably took no longer than 3-6 months for Ammon's complete round-trip to Lehi-Nephi and back.
4) The arrival of Alma1 in the land of Zarahemla was about the year 481.
The Lamanite army pursued Limhi's group into the wilderness, but after two days they found themselves lost (Mosiah 22:16). Eventually the Lamanite army found the priests of Amulon and together they went "in search of the land of Nephi" (Mosiah 23:35) and encountered Alma in the land of Helam (23:25, 35). The land of Helam was a little over 8 days away from city of Lehi-Nephi. Mormon mentions that part of the Lamanites not only went back to that area (actually Shemlon) but returned with their wives and children (Mosiah 24:38). Enough time would pass that (1) the Lamanites would take possession of the lands of Amulon and Helam (Mosiah 24:2), (2) the language of Nephi would be taught among the Lamanites by the priests of Amulon (Mosiah 24:4), (3) the Lamanites would increase in riches and begin to trade one with another (Mosiah 24:7), and (4) Amulon would persecute the people of Alma (Mosiah 24:8). After this period, Alma's group escaped and took 13 days to reach the land of Zarahemla (Mosiah 24:20,25).
We can estimate that a number of months passed between the arrival of Ammon and Limhi in the land of Zarahemla and the arrival of Alma's group. However, this interval was probably not overly long; otherwise Mosiah2 would not have gathered his people together upon Alma's arrival to read both sets of records (Mosiah 25:5-6).
Therefore, even though the scriptures tend to mesh the arrival time of Alma1 and Ammon and Limhi in the land of Zarahemla, it is possible that Alma could have arrived in the land of Zarahemla 6 months to 1 year later than Limhi (in the year 481). If Alma left Lehi-Nephi in the year 460 and arrived in the land of Zarahemla no later than the year 481, then Alma spent at least 21 years (460-481) in the wilderness [estimated minimum].
To figure an estimated maximum amount of time that Alma might have been at the waters of Mormon and in the land of Helam, we consider the following possibilities:
1. If Alma was a "young man" of 30 instead of 32 when he fled, we can add 2 years.
2. If Benjamin's last 3 years (Mosiah 6:5) were not the 3 years of peace of Mosiah2 (Mosiah 7:1), we can add 3 years.
3. If Ammon's trip takes much longer (1.5 years and not 6 months), we add 1 year.
4. If the Lamanite occupation of Helam was for a longer time (1.5 years and not 6 months), we can add 1 year.
Thus, an estimated maximum time for Alma in the wilderness is 21 + 2 + 3 + 1 + 1, or 28 years.
It might be interesting to note that according to the proposed chronology in Appendix A, Alma1 spent two years at the waters of Mormon and nineteen years in the land of Helam. [Alan C. Miner, Personal Notes]