Using entire interview time a must?

I recently had an interview and the interview time was slotted for 55 minutes. My interview was a little over 35 minutes. I'm used to coming from private and i try to answer interview questions as fast and as succinctly as possible. I don't like to blabber on about things to fill the time. I try to get my point across and that's it. It is a bad thing if my interview doesn't go the full length of the time? or is it ok?