Lastly, everyone's sense of how months work is completely distorted.
A month from January 1st is February 1st, not January 28th. January 28th is 4 weeks from January 1st, and 4 weeks do not necessarily make up 1 month. Unless Crytek can't use calendars nor know grade 2 months of the year, the achievement should unlock for most people on September 22nd (those who started March 22nd).
The method going around where it's 5 months + 4 weeks doesn't make sense. It uses the logic that the first 5 months are counted as ACTUAL months and the last month is counted as 4 weeks. Why on Earth would they do that?
I realize it will take 5 months+ to prove me wrong, but seriously, it makes no sense other than the way I explained at the top of this post.