The biga worked! Rather, it certainly got active during the night. The recommended ferment time is between 12 and 24 hours; I mixed it and set it to rest yesterday around 12:45, and got back to it around 7:45 this morning. Within those 19 hours, this transformation took place:
And it smells SOUR. And this is GOOD. I continued on to the next step of the recipe, hooked it for 8 minutes, and now it has the consistency of caulk. It’s sitting under plastic to double over the next 90 minutes, then to be separated and proofed once more before baking.