They're probably about 6 months away from shooting, at the very least. Still a lot of time left for casting, I believe. Some casting actually can be done pretty much right before shooting starts (it's not unheard of to have a major part cast with less than a week to go). Unless the choice of actor for a role has an impact on pre-production in some way (including, but not limited to, investors or studio requiring big names), a significant factor in casting is the availability of the actor. The stars of this project are Johnny Depp and Tim Burton, so I don't think there's much concern with getting other big names.