After flowering is over through Winter dormancy. Take 3 or 4 eight inch cuttings just below a leaf node. Remove any remaining leaves except for a top couple & plant half their length deep in a pot. Cover with a plastic bag. Put them on a North facing windowsill & remove the bag at the first sign of new growth.
You should have a choice of which to harden off & plant in place by Spring😊

the RHS site suggests hard wood cuttings after the leaves have dropped and before they break bud in the spring.
https://www.rhs.org.uk/advice/profile?pid=387

having said that I have take semi ripe cuttings from august onwards. I cut 6 6" stems that had the bark turning brown [becoming 'ripe']. I strip off any leaves except for the top 2-4 leaves. I then push them around the edge of a 9cm pot of gritty compost. watered and left in a shady spot in the garden. I just make sure they don't dry out.