As a general rule, it takes 15 days for the response to an application (see this link); and as you need to provide your travel details the consulate is aware of your deadlines - this however does not trump their internal process.
You don't get the visa after the interview, the date when you can collect the visa is given to you by the consulate or VFS.
The experience that I have with Schengen is that the embassy calls you when your passport is available for collection this doesn't mean that the application is approved.
Do submission of papers and processing biometric confirm the start of
the process for Visa? I am perturbed about dates.
The best way I can answer this is to describe the visa process:
There are three steps to this process [a] validation of application, [b] collection of biometrics and [c] interview.
Once you arrive for your appointment, the officer (or agent, in the case of VFS) enters the information on the paper application into an electronic system, your supporting documents verified, your passport is scanned.
Next, your fingerprints are scanned to be attached as part of your application (this should happen only on your first application, but I believe based on the nationality they scan the data each time). Any fees required are collected and you are given a receipt and a token/reference number that represents your application.
If you are lucky enough to submit the application at the embassy, you may be interviewed at the same time (like I was). This interview generally asks questions that are not on the application form itself. However, these days most foreign missions are outsourcing their processing and unfortunately these outsourced agents are not authorized to conduct interviews - which is why you have to get a separate appointment.
Next, your documents, photo, passport is submitted to the visa issuing center. This may or may not be in the same country or city where you apply. For example, in Kuwait for the Netherlands; the visa is issued from Amman, Jordan.
In India, there may be a central processing station as it is a very large country.
The timeline given to you of 15 days takes all this account; and it starts from the acceptance of your documents. If you are a first timer or there is any issue with your application, it may take upto 30 days and in extra ordinary circumstances, 60 days.
The good news is that the agents/officers know the typical processing times for that station and will give you a very good estimate.
The first time I applied for my Schengen visa, my passport was delivered 7 days before my flight departure.
The second time, it took only 10 days and I got it well in advance.