Hi

Spring is best so late April into May (not earlier) , so a light pruning as you may lose flowers if you give it a good hair cut , but if over grown may also be cut hard back to rejuvenate the plant (only if its established) as the shock of hard pruning may kill it.

Its a choice shrub to have any chance of a photo

I cut mine back immediately after it finishes flowering. You can cut it very hard (like a buddleia) to stop it becoming woody and top heavy.