It is a mystery

You know how someone who likes what they do will realize they're saying too much in the way of trade secrets and reword three times and then shut up abruptly? The baker on that tour was like that.

They settled on "until it's doubled, and a week is too long"; what I recall from their setup (big colour-coded dough tubs in a custom fridge; it's apparently bad to mix strains of sourdough) is that their stuff tended to run between fifty and eighty hours. Only wheat breads got overnight-or-a-day, which I took to mean something like between ten and thirty but maybe twenty hours. And they did it by volume, rather than time. ("is it touching the lid?" seems to have been the test.)

(This was a small commercial bakery with its own bakery storefront; they didn't make much bread by commercial standards but they charged a lot for it and stayed in business, so I figure they have to have known something.)