Passport stamp timeline

[Cane]

If all goes well, I am assuming that a few months after the medical is done and results sent, one receives a letter from the Regional Program Center indicating approval of application, and asks for the passport to be submitted for the visa stamp? Is that how it happens? And once the passport has been mailed, how long does it take for the RPC to stamp it and return it? The RPC for me is in Buffalo and I am outside the US (but as per the instructions on their web site, I will be using a close relative in the US as intermediary).

Thanks
Cane