Hey! Welcome to the land of the obsessives! High fives from another Matthew stalker. ;D As far as time-line is concerned, each season is approximately a year, though the cliffhanger finales warp time at the beginning of every season. The show premiered in 2006 so that's generally when it's assumed to take place. Unfortunately, as many here have already stated, this show's time-line and continuity errors are egregious. (Don't even bother to try and make sense of Hotch's backstory, it'll turn your brain to scrambled egg). Fudging works pretty well since for the most part your guesses will be just as good as the rest of ours. :)