This is a different version of a comment I left at Wikipedia.... As noted in discussions at Reddit and elsewhere, George Michael and Maeby at the start of season 4 are 18 years old, instead of 16, even though the season begins at exactly where season 3 left off. This retroactive continuity is made very clear by George Michael soon leaving for college (and first there being somewhat of a graduation party for him) and the development of the Maeby-staying-in-high-school story. There is still some confusion about how, if season 3 ended in fictional 2006, we can still end up in fictional 2012 at the end of the season 4, since it seems that only 4-5 years have passed.
Here's my take, or at least the first sketches of how I would solve this problem. George Michael only went to college for four years, though some at this Fandom site have tried to stretch his time in college to 5 or 6 years. It's said that he had a "semester abroad" (not a full school year) his junior year (the spring semester because we were also shown him participating in the kissing study in the fall semester) then came back after that summer.
If you follow the Maeby story closely, you'll see that she has a "sophomore senior" year and a "junior senior" year (that is, second and third senior years after purposely flunking her first senior year), but then she seems to give up on the idea, so there's a year when she's not in high school, only to return again for a "final senior" year; note that the narrator does not use the phrase, "senior senior" year for this third additional senior year because that at that point in the joke the play-on-words falls apart. If she had a fourth additional year, it would not have a name that fits because because the first additional senior year was her "sophomore senior" year, the second "junior", and the third "senior". So then why have her take a year off? First of all, it helps her story, because the viewer has to doubt how committed she could have been to the notion of staying in high school (even if it gave her something to do). Secondly, it accounts for Maeby's four years.
Therefore, the fourth season, at least when looking at these two characters, seems to start in 2008, not 2006. This date still works for the housing crisis. The only thing that stands in the way (the only thing that immediately comes to mind, that is--who knows what else I'm missing) is the real-estate agent (played by Ed Helms) saying "it's 2006." But that can be a joke on his part, because he can't believe this couple with no money is buying a mansion in 2008. If that takes place in the summer of 2008, right before the general economic crash, but after the housing crisis had begun in August 2007, it would make sense that he would make that joke, as well as the joke about him being selling houses to people who can't afford them. When we get to other characters (e.g. the check that Lucille 2 writes dated June 2008)... I'm not sure yet how to explain away all the inconsistencies.
I will say, though, that I think we should focus on making the characters' timelines match each other, rather than worry too much about the fictional timeline matching reality (except insofar as the characters themselves bring those historical dates into play, as with the "it's 2006" joke). In a fictional universe, especially one as highly developed as Arrested Development's, you can say that certain historical events took place differently--for me, that's no big deal. For example, an important date in the season 4 timeline on this site is Buster Bluth re-enlisting in the army on the very day that "don't ask, don't tell" was officially ended. This date can be different in the fictional world--why not?