I've broken the 20 percent mark, and only 23% of the way through the working month. (Omitting Sundays does put a cramp in my word count, but I'll make it anyway.) Over ten thousand words into my novel, I still haven't gotten to the main action, and that's OK. I've been fascinated to see what the early bit has turned out like.
For anyone who hasn't tried this experiment before, I totally recommend it. What a rush!