Blackberry flow is basically over here (Jeff co.), but I see my bees still bringing in quite a bit no nectar, I am not sure from what. Still some (gray) blackberry pollen and the third round of dandelions is blooming now.
I feel that it is important to feed early fall and then stop feeding so the queen will stop laying late october or so if you feed much past mid-late september, the queen will still be laying too late in the fall, the brood nest will be backfilled with syrup, and the bees will not have a good space to cluster. You want lots of young bees going into winter, so heavy brood rearing in the next month is good. Don't let them backfill too much. Move things around if needed, add empty drawn frames to the edge of the brood nest if possible.
I will feed heavily as soon as I see a real dearth which normally I would expect now but this has been a really late year. I am feeding nucs /weak hives now and will probably pull last of the supers in 2-3 weeks at the latest. If you are treating you must do this earlier (NOW). We don't have a much of a fall flow, unless maybe you have a big patch of Japanese Knotweed nearby. Once the hive weighs as much as you think it should, stop feeding, hopefully they will start to shut down brood rearing about a month later. This may not apply to some strains of bees (ie Italians) as well, some will rear brood all winter long, you may have to feed these more. I am planning to try dry sugar on newspaper on the top bars as emergency feed this year. "Mountain camp method" on Beesource, michael bush explains it on his site
This is what I do in Western WA, very location dependent. Ask your local bee club /et cetera