When it's flowered. Then, as soon as it comes into new growth, give it a feed so it maximises the use of what leaf it has left. If they're growing well, then like most shrubs, they'll respond to pruning, but it may take a couple of years' careful removal of some of the oldest wood to recover fully to the best shape.

Yes, they respond well. I've done mine over two years - just hyping myself up to cut the last tall bit.