For more flowers, cut buddleia in early spring. Early spring is a good time for pruning, as you do not endanger the formation of flowers.
If you cut too late, the flowering will start later. The harder the prune, the more flowers the bud dleia will produce. In late winter, the buddalia tolerates severe pruning at around knee height very well. Only when it gets too big or becomes bald is it cut back more severely.