In book 13, Tobias said everything had been going on for about a year. That's 13 books in around 1 year. If we used that as some kind of measurement, then two years would be around book 26. But going like this to book 54 would make it more like 4 years. However, it's stated that it's been about 3 years at the end of the series.
So when is the two year mark? It's not really a big deal or anything, but it's something to talk about.
I was tempted to put this in the random questions thread, but no one ever pinned it and I think it's down past page three.