You could move it now if there's no frost in the ground.

Get as much root ball as you can and cut back hard this years growth. It should grow away well in the spring

Best times imo would be early autumn or early to mid spring

I'm planning to move mine in the spring. It's just used lot of energy late in the season by flowering so I don't want to put it under stress until after the winter

Now or in early spring. If you need to move them now for some reason then that will be fine. If you can wait till spring that would be my preference but there shouldn't be any big problem either way.

I'd do it in spring just before it starts int regrowth. you can then split/divide it if it is a big clump. Moving it now when there is some live topgrowth will not do it any harm but you will get wind rock etc and it may be slow to root now the temps are dropping.

Thanks for all your help everyone. I think I will leave it until spring as it was covered in flowers until only a few weeks ago and was huge so will have used lots of energy. The size is the reason for moving it as it turned out to be too big for the space. I am planning to move to the end of a raised bed where I can consider what to plant in front of it that will not get overshadowed.Also it had a tendency to lean so it can be given some help as it will be in a corner with fence at both sides. It died back to nothing last winter after its first summer and I thought it had gone for good but was delighted when the new growth showed in spring and it has been very happy this year, it is Aster Lady in Black.

That reminds me to move my Lady in Black. she has been towards the back of the border for several years and needs some tlc.