Initial proof

Toast

So the recipe says to mix and “let double” for 8 to 18 hours. How do I know if I let the dough overproof? I prepared the dough at noon and checked before going to bed but felt maybe I should let it continue to rise. (My previous breadmaking experience taught me to allow the fermentation to develop longer.) This morning it looks like it’s fallen and has a strong alcohol smell. Yikes! So where’s the sweet spot? How do I know when’s enough???

it's not clear whether you did preferments, levain, or straight yeasted dough. If it's preferments, just proceed with the recipe. Alcoholic smell is okay with poolish preferment. If it's levain, since most people do liquid, seems like won't be the case. As for straight yeasted dough, do coil folds, if still elastic and extensible, proceed with the recipe. Otherwise, pizza time! :D

A recipe's time range of 8 - 18 hours doesn't mean that any time in that range is all right.  It means that the fermentation might take 8 hours, up to 18, or somewhere in between depending on a variety of variables. In addition, some doughs will have a broad span of time within which they will be usable and some don't.

For example, suppose your dough would have been ready after 10 hours.  Leaving it for another 6 - 8 hours would way overferment it.  That seems to have happened to you.  But if it would have been ready only after 16 hours, an extra 2 hours probably would have been fine.

How to judge? Partly it comes from general experience with making bread, partly from the suggested times, and partly from experience with your own starter and this kind of flour, etc. If the dough has risen well, nearly doubling in volume (this can be hard to estimate) and softening so that it jiggles a bit when gently shaken, it is probably ready or nearly so.  If it has just gotten started rising visibly, it's nowhere near ready.  So if the dough or levain didn't seem to start to rise until 7 hours, the rest of the rise will take a long time too.  If it starts rising in say 3 hours, it will probably be ready in 6 or 8.

What to do if you run out of time and you aren't very sure about the state of the dough?  Refrigerate it for the next day.  Then bring it out and let it warm up and finish fermenting.  The bread will taste better, too (although it might get more sour than you like). The dough will also ferment some more in the refrigerator as it chills down, so it might be ready to use at that time.

TomP