I was invited at a conference to give a contributory talk. I was given 12 minutes to speak and 3 minutes for QA, but to keep my talk simple I didn't go in details (probably I spoke faster also) and finished it in ~10 minutes. I know this somewhat disturb the flow of the schedule but it also gives more time for discussion. I want to ask, what is the general impression in such cases. Is it bad to finish your talk early?