Yep, for me at least, I try to stop rooting mid-September. That's not to say I won't take cuttings after that, since I often do because of having to bring in large plants, and thus needing to trim them. I will stick those (late) cuttings into coarse perlite, knowing that the chances of rooting them is slim. Mother Nature is calling for them to go dormant and being in that dormant cycle is just opposite of being in a growth/rooting cycle. These late cuttings will just overwinter in the buckets of perlite. Not all these cuttings will make it over the winter though. They won't necessarily rot, they just get stone-hard from too much water loss. So plumeria can go hard just as easily as they go soft. Dead is dead either way.
I agree with all that has been said. The main thing is to not let any rot get into your plumeria.
