Dahlias are naturally late summer flowering. However, they love a deep, rich soil and hate being dry. You might of let them get a bit on the dry side during the july and august hot spell, which can inhibit their growth.

If the weather stays warm, you might get a good flush of flowers right in to November,

Mine have better flowers on now than they had all of September Badfish. Don't forget to deadhead as the old flowers die Lynda.

Depends on the variety as to how they grow.
Most "exhibition" dahlias that are bought from reputable suppliers will grow well in any garden.
They can be in flower from July onwards.

Thanks to you All.For great advice.