While many hydrangea bloom on old wood, some bloom on new wood. The Hydrangea Paniculata varieties are such that bloom on new wood. Before pruning be sure that the variety your are pruning is a paniculata variety. As such, now is the time to prune them down to about 12 - 18".
It's time to cut back you butterfly bush (Buddleia davidii). It's best to cut back to 12 - 14".