Just a reminder (or notification to those not in the States/Canada), Monday is Labor Day, and thus time to speak to Calendar Man again, if you're looking to do this legit or want a timestamp.
And seeing as the game was released in mid-October, how many that have been doing this legit will be finally finishing this achievement this time around?
Unfortunately, I got the game for Christmas, but didn't get to playing it until New Years. Not knowing at the time if the dates were just for the '11-'12 year (and thus were missed) or were flexible, I did October-December's offline, but have been doing legit since. So this is it for me, although a part of me wishes it wasn't.