A brief downtime will launch the new content.

According to the Official Free Realms Facebook Page, the wait is over: Sunstone Valley will launch tomorrow!  Ambassador Amnerys posted on the forums:

We will bring the Free Realms PC servers offline on Wednesday, September 19, 2012 at 8:00 a.m. PDT (San Diego Time) for a Game Update. Anticipated downtime is around 2 hours. What's coming? It's the big one! We'll see you in Sunstone Valley!

Here's our handy Time Zone Conversion Tool to help you plan!