When it's ready.
To be clear: this site is doing very well so far. Not just by the numbers, but in how the folks here conduct themselves and handle increasing amounts of traffic (as we've seen over the past couple of months with the start of the school year). I've written a bit more about this here.
So what are we waiting for?
So from this point forward, the graduation date of a site will depend heavily on having enough users with sufficient reputation to properly lead and govern the site. It’s much more important to graduate a site when it has become self-sustaining, and has established a healthy community of avid users, closers, and editors — rather than imposing an arbitrary 90-day limit.
-- When Will My Site Graduate?
As I said, there's been a notable uptick in activity over the past few months. Here's a graph of questions from new users over the past year and a half:
As you can see, last year caught a nice little bump in October - this year, that kicked off in September. Folks are having a much easier time finding this site, and... They're making the most of it. That's awesome - but it also means y'all have a lot more new folks around, and the distribution of reputation (and associated privilege) is a little bit skewed.
Assuming you have no major problems handling the traffic and associated new-user problems (potential drop in the quality of Q&A, etc), I see no reason why this site couldn't graduate in the near future. You'll get the chance to do some more introspection in a few weeks, and we'll talk over the results here at SE.