It is actually 6 months, but that can vary I believe. If you start your tank out with cured LR, and LS from another tank you may be able to get one a little sooner.
One LFS I went to was setting up a display solana tank(so everything in it is NFS), and they put a LTA in there after 9 hours of the tank running. I'm pretty sure they started it with cured LR, LS, and water from one of their established tanks though. They have had the LTA in there ever since, and it has been doing really good.
Lighting is the main issue with anemones.