If I plant an Autumn Joy cutting now, do you think it would actually bloom this September or would it need a year to establish itself?

Welcome to ATP!

Last year, I planted some Autumn Joy cuttings around mid-late April. Most did flower last year, although a couple did not.
However, the plants and flowers were nowhere near as tall or wide as established ones.

Sue,

I've had the same results here. You might try grouping several cuttings in the same planting area or pot, then if blooms stalks do form it'll give a fuller effect in this first year. You can very easily separate them in later years, as the need arises.

Thank you both so much!

And just took this photo, snowing cherry blossoms!

Glorious!

That's way prettier than our snow!

Yeah, pretty crazy weather, we got absolutely no snow, not even in the mountains! So sad for the skiers