I know that Clematis Fireworks should only be lightly pruned in early
spring. However, I neglected to tie it to the fence properly, and now it's
a tangled mass of shoots which have sort of flopped over in a big round
ball, dangling half on and half off the fence.

I could try and untangle the mess but the stems are really brittle so I'd
probably break most of them, so I'm thinking that I could prune it back to
almost ground level and start again.

So, should I prune it now and hopefully get some growth out of it before it
dies back in autumn, or should I wait until spring to prune it back?

Thanks.