Best time for any cuttings is when you can get them.
Second best time depends on your skills and propagation setup.
Soft cuttings (spring) root quick but need humidity control to survive because leaves are transpiring water which cannot be replaced until roots form.
Medium cuttings (after flowering) are hardier but still need humidity control.
Dormant winter hardwood cuttings (after leaf fall) are easiest as there are no leaves to use up water but they do take a bit longer to root.