I understand that Stanford is now offering a five year PhD as a reduced time to finish. This is ridiculous. In the UK the standard time to complete a PhD is three years. I did mine in two. If you take seven years to complete a PhD you are either twice as lazy or twice as stupid as somebody who does it in three years. Even five years is an awful long time to write a single book without any other obligations all the while receiving extensive advice on how to write that book from trained professionals. Honestly, where I got my PhD (SOAS) the dissertation is limited at 100,000 words. So if you write 200 words a day you can finish the first draft in no more than 500 days or less than a year and a half. That gives you a year and a half to edit and polish a short book manuscript. It can of course be done even faster. If I were not the laziest man on earth I probably could have finished writing my dissertation a lot quicker than the two years it did take me. Five years is not a short time to write a PhD thesis. It is an extraordinarily long time by the standards of most of the Commonwealth. Anybody who spends seven, eight, or more years writing a PhD dissertation is not making good use of their time.
Update: In response to the comment below I am clarifying that I am only talking about PhDs written in the field of history. It does not apply to any other field since I have no first hand knowledge about what those fields entail. But, writing up a short monograph on an historical topic should not take over a half a decade if that is your main focus during that time.