Atlanta is slow. I filed 6/29, fingerprints 7/26, in line for interview since 7/30. Received yellow letter 10/2.
People who filed in the latter part of May are starting to receive their letters, so I'm estimating another 3-4 weeks to receive my IL, and it will likely be scheduled for a month after I receive it.
Following that logic, you can probably expect to receive IL some time in December, with a January interview.
Might be sooner, might be later, but that seems to be the emerging pattern for the Atlanta office.