Mainly I think that it depends on how well-formed the piece is in your mind before you write. If, in a sudden bout of inspiration, the idea justs come to you, fully formed, then much less time will be needed in order to polish and/or complete it. On the other hand, the opposite holds true for those who have a general idea what they want to write about but have to struggle to find the specific process or words to express it.
Space: the final frontier. These are the voyages of the starship Enterprise. Its five-year mission: to explore strange new worlds, to seek out new life and new civilizations, to boldly go where no man has gone before. — Captain James T. Kirk
