What controls leaf senescence in deciduous tree species, and how can I predict it?
One can sometimes notice street lights delaying the annual shedding of leaves in some species (a well-lit branch will be mostly green while the rest of the tree is turning). So at least part of it would be day/night length in at least some species.

I would expect, however, that the answer varies based on species, genus, and/or family, and that there are probably multiple causes at work (one obvious alternate cause being temperature). Just going from memory of my personal observations, years when autumn weather patterns start earlier do tend to have trees turn and lose leaves earlier, so it's not all day/night length.

Drought is also a factor. I live in a seasonal-rainfall part of the world (US Pacific Northwest), and if summer is drier than normal (and normal is pretty dry), by mid-August many of the native deciduous trees will be starting to drop leaves. (Not all of them, but some of them, definitely more than just a few, will be turning and dropping.)