It is an early access release only available for those who registered to test out early versions (basically RC versions) of the OS before it gets released to the wild public. So in general it takes around 1 week when no major issue is found.
Yes, Prasanna & Joseph. As I have not installed any OS update after getting my phone on July 25, I thought it was a latest update and asked immediately without checking. I think this update importantly having indic languages typing support and essential to the Indian market. That might be reason to have early access release on our devices before they announced it officially.