Number of days on multiple entry Schengen visa

[Gaurav Doshi]

I just got my Schengen visa from Austrian consulate in LA. It's a multiple entry visa, valid for a month (May 15 to June 15). I had submitted a 12 days itinerary when I applied for the visa, as a result, the visa also mentions "duration of stay" as 12 days. I am wondering if I need to take that seriously.. As long as I am still travelling between May 15 and June 15, can I extend my itinerary and and stay longer than 12 days?

[immihelp]

Yes.