In article , Martin Sykes
writes
You'll get both answers depending on people's preferences. I personally
leave everything until the last possible minute in the belief that the dead
heads provide places for stuff to live, food for the birds and some shelter
for the new growth.

When you do come to cutting back the hydrangea it's usually a good idea not
to do it too hard initially so that if you get a late frost which kills the
tips you can prune back again to a lower bud.

It's all a matter of personal preference. We tend to prune our
hydrangeas very hard in late autumn as soon as flowering has finished.
That gives the stems plenty of time to heal over before any frost is
around and they can put on their spring growth without any disturbance.
We are rewarded every year with a glorious display of bloom.
--
Alan & Joan Gould - North Lincs.