Hi Maureen, you can apply it any time. It will get taken down by worms over winter to enrich the soil. Some people like to mulch more in spring to keep moisture in, suppress weeds and make everything look tidy, but there are no rules!
I haven't quite got leaf mould but I do have several bags full of breaking down leaves. Can I add these as a lower mulch layer to flowerbeds and then cover over with some rotted manure?
indeed you can Lucid, and , as fairygirl says, the worms will do the rest
I'd leave them Jo, but I'd make sure they're not throttling plants and I'd probably remove anything dubious looking or diseased first
The plus side of apply it now is the fact twill your plants will have a nice comfy blanket thoughout the winter