Holly Bush hedge - hacking shorter - timing

I'm pretty sure I can cut back/down my holly hedge a lot and it will come back. Question on timing - better now or winter? Middle TN, so we'll get several hard freezes. I know the very new growth can die off in a freeze, I've seen it do that but it still comes back. I need to cut them down a foot or more, probably past the current leaves. Front needs cutting back too, so it might be a brown dead looking hedge for a bit. Don't really care about that, just want to make sure I don't fully kill it.