I have a quilt that took me about 5 years to piece. I just would take it out, work on it a tiny bit, and put it back. I even gave it to my sister and she cut some strips and gave it back. I don't know why it was so hard to birth that one, but it was. So the top and backing are done now, but it still isn't quilted. I think I am at 6 years and counting on that one. (It's pretty, though!)
Others I have finished in 2 weeks. I guess it just depends on the quilt and whether or not it has a "due date". That usually speeds me up. I have made very simple tied baby quilts in a weekend, but big ones take at least several weeks. Usually I work on them for a year or so. I have about 20 UFOs at any given time. Maybe I am a bad example...