We have received some information from a trusted source surrounding
upcoming release of iOS 5 that could help pinpoint a more specific
launch time frame for the iPhone 5. Starting off, we have been told that
even though Apple seeded iTunes 10.5 beta 8 last week, iOS 5 beta 8
won’t be released until this Friday. After beta 8, Apple will introduce a
Gold Master build on or around September 23rd as has been rumored. We
believe that build is what will be loaded onto the already-assembled
iPhone 5 hardware currently waiting for final software in China. Apple
will then request that carrier partners give technical acceptance to the
Gold Master by October 5th if there are no issues with it. What’s not
clear is what Apple will do if the Gold Master doesn’t pass technical
acceptance for some reason, though odds are it will still be loaded on
the iPhone 5 at launch with a software update made available almost
immediately following the device’s release.

Source: iOS 5 beta 8 coming this Friday, GM on the 23rd, iPhone 5 launch early October as rumored?
BGR: iOS 5 Beta 8 due this Friday, Gold Master September 23? | 9to5Mac | Apple Intelligence