My experience is that I absolutely have to see it as a reader, like Bufty says, and that takes months--enough time to start the planning and research and even the writing of the next book, unrelated to the one just completed.
During this period, I can write myself notes of things to add or delete, facts to check, additional research that might prove useful, but I cannot open the document, not to read, not to peek.
So I give myself a one-month minimum vacation away from it, plus a week for every ten thousand words, give or take. (Note that I do not have an agent or publisher drumming their fingers waiting on me.) Usually it's three or four months at least, enough to get a good start on the next book, before I return--and it's like someone else wrote it. All of a sudden I see where I ramble, authorial intrusion, inconsistent character behavior or motives, and all kind of lesser flaws, too.
As everyone's saying, do what works for you. You'll know within a few pages if the work feels familiar or not, and if it's too familiar, you won't edit/revise/rewrite the same way you will when it's not.
Maryn, who really wants to peek