It's very interesting reading these responses and everyones impressions. Thanks for all the thoughts coming in.
I should note that I'm especially interested in the retrospective look back and perspective from thoses who have been there. Most authors probably haven't thought much about it in terms of total time, as people seem to think in terms of elapsed months. Of course, I don't expect to plan any schedules for my project based on these answers, and it will be done when it is done. (Or as pointed out, whenever I call an end to it. and my hope is that I don't have to give up at some point due to the realization that the story can't be saved.) But all the answers are giving an interesting angle on the whole question.
Hopefully, I'll be providing some thoughts myself in a year or two.
