L&C

Hi Sheepwalk,
I have already return all package 3 forms to embassy.
And now waiting for documents, e.g I-134 with supporting documents.
Upon collection all required document, I will need to send DS-2001 is a form to notify my regional embassy upon ready for interview.
Re 2: Once pass the interview, the application (K1 Visa) will be approved immediately or within 7 days.
As per my local embassy's reply, my interpretation is If they don't receive my notify form that I am ready for interview, they will send me a reminder.
The reminder will advise you that you must response within 60 days in order to pursue your K-1 visa application and avoid termination of your registration.
Since, the application for K1 Visa will be terminated if applicant does not response to the embassy within 60s days.
So, I don't think they will automatically extend the application without any response from applicant.
My suggestions are
1. Response to the reminder with your extension letter
2. Send the extension letter in prior of the reminder
Hope it helps. There is a chance that different local embassies have different procesure, so, the better seek for local embassy's advice.