Here's what's missing from this conversation.
There is a difference between chems when it comes to temps.
One formulation might be an amine compound which is recommended for higher temps as it has less potential to burn a lawn in the late spring through summer.
Then there are ester formulations. These chems are better for mid-late fall apps. You can use it in extremely "cool" conditions and down to the lower 40's for temps.
Some would say doing a late fall ester app is going to yield better results on the hard to kill weeds.
But even I have used amine formulations clear up until late October with great success.