There are many variables to answering that question. I read somewhere once, someone breaking it down into total man hours but I thought that figure was meaningless without a context.
How many people are working on it in each phase? How much money you have to throw at it? A specialist can do things in 1/4 of the time a "jack of all trades" guy can. Comes down to my sig; fast, cheap, good, pick any two.
Special FX? Lots of ADR? Is there an original score?
Are there hard deadlines or is it soft? If it's soft then I have seen guys take well over a year of earnest hard work at just the video editing. On the other hand, if the production phase was done well, a production could be cut in a week or two. Again, just talking the EDL here, nothing more. Depending on how complex the cuts are, a negative cutter could take a week or a month to do his part.
Audio is an area that often takes more time then anyone expected. Composing scores, dialog editing, sweetening, foley, ADR, and mixing all take a fair amount of time.
If you don't want to work as intern on another person's production then the quickest way to learn how to budget your time and money is to do a short and learn from that experience.