I started writing my MSc thesis 8 months before I submitted it - but then I was doing a research degree and the research project/dissertation was worth 100% of the degree!
It was crazy though - 6 chapters, 100 pages (inc. 5 pages of references) and 15,500 words. I was aiming to submit it by the end of September last year, but it got to September and I still wasn't done. My supervisor thought I could probably get it finished in a couple of weeks of the end of Sept... I finally submitted on December 19th 2007, had my thesis defence on January 7th and moved to the US on January 15th!!