Let's see, I've been working on my comic for 3 years, I've (almost) finished 3 chapters so far. I'm not quite sure how many more chapters I have left, but I'll guesstimate that it's be another 6 or more years till I'm finished... that is if I continue to hold up a fulltime job while working my comic.
Sometimes I think "wow, I'm going to be in my 30's by the time I finish a comic I started in my 20's. Would I even be able to make that kind of commitment?", but as long as I'm enjoying the process of working on it that's good enough. I know I'll feel pretty awesome when it's done.