I don't like to put a strict timeframe on an issue that is so subjective. For instance, I would consider a woman who has been using OPKs, temps every single morning without fail, goes to acupuncture, and takes twenty supplements daily for six cycles more in the LTTTC "mindset" than a woman who has been taking the "just relax" approach for two years. That being said, I think of most women who have been trying for around a year as LTTTC.
LTTTC to me is where you've gotten to the point where you've come to the realization that it may never happen for you, but you want a baby so bad you still keep trying month after month even though it gets more and more painful to keep getting AF/BFNs every month.