I do it in early September...
It's a kinda a slow transformation at our house. I start to transition out my summer flowers from the big planters and replace them with mums.
I put up my fall wreath, and I hang these fall teardrop decorations from my lights on my garage and on either side of my front door. They're really pretty with gourds, mini pumpkins, fall leaves etc I get a lot of compliments on them.
In October, sometimes I do the whole cornstalk, hay bale, pumpkins, mums etc around our lamp post or mailbox. And some years I don't! LOL! Just depends on my mood, how organized I am about it etc