Blackbird - I had a 4 month wait between my Spec Testing and Assessment Day. I live about 8 hours from Townsville (where I had my testing and interviews) so it took a bit longer for me due to travel and work.
It may seem like it is taking a long time, but use the time to research and read as much as possible. The more you know for your Defence interview the better your recommendation may be, and the more motivated you appear to the interviewer.