obviously it was vetted before the cookbook was publsihed but I am super careful about food safety and curioous about how this is ok.
I'm no panchetta expert, but the legs of various prosciutto at my local high-end supermarket and also at my local cheese shop (Hello, Stinky Bklyn!) sit out completely unrefrigerated. And if you go to Spain or Italy you see these out everywhere with nothing but a cotton dishcloth covering them.
Bottom line, salted, cured meats like that likely take a lot longer than 18 hours to go bad.
(Heck, I'm so NOT a pancetta expert that I mispelled pancetta above. Yikes!)
In my version, I sub a thick slice of prosciutto for the pancetta and it only stays out for the final rise of two hours.
I would agree with Peter. Food safety recommendations to keep things like pancetta refrigerated tend to err on the very conservative side. Because pancetta has been cured (an ancient process designed specifically so that foods wouldn't go bad back when there were no refrigerators), it should actually be fine unrefrigerated for several days, especially if it then gets cooked, as it will in the baking of the bread. But, if you're nervous you can go with TiggyBee's method and just work the meat pieces into the dough before the final 2 hour rise.