Found this on WDW magic:
4 May 2006: Finding Nemo - The Musical opening dates
According to a casting session being held in New York for actors to take part in the new show, rehearsals are set for 18 September 2006, first previews on 5 November 2006, with the show opening on 12 November 2006. Remember, this has not yet been officially confirmed, and as always, thing are subject to change.
~good news for those of us going down during Christmas time!