September is the month when 40nm next generation architecture, something we call GT300 should get taped out. We can confirm that this has already happened and that some VIP analysts and investors have already laid eyes on this DirectX 11 card.
If you do the math, it takes at least six weeks after tape out to release the card and get it ready for full scale production and if the tape out occurred on the first days of September, the full production can start in the middle of October. It is always at least six weeks.
Nvidia was always aiming for a launch close to Black Friday, the first Friday after Thanksgiving and this year it is on November 27th. It is important to launch the product before this date as most of the shopping is usually done around this date.
If something goes wrong with Nvidia's schedule, they can easily start shipping in December time, but the worst case scenario is to show the card in the next few weeks just to keep the fanboys comfortable with waiting for the next Nvidia's DirectX 11 offering and ship it as soon as possible.
You might remember they did this with Geforce GTX 295 last year, and it did work for them.