I always wanted to finish within 3 years and thought it would be the end of the world if I didn't. But this didn't happen - I have been doing mine for 3 years and 5 months and the end is in sight! No one who started with me at my uni has submitted yet. I have publish 2 papers, presented at 4 conferences and been teaching which does take time and energy away from the PhD. However, I have met a couple of people who have completed theirs in 2.5 years! So it is possible, but it means being focused and not running into any time-consuming problems.