I see that you are in CA 19. From Sunset I would gather that you're not a lot different from here, so I'll try to answer your question..... and I'm assuming you're meaning S. leucantha.

I leave the top growth on until it warms up in February/ March, then I prune it to the ground or the bottom set of new leaves. If I prune too soon the tender new growth will turn black. Then in the summer -- if they're looking too ratty -- I prune them back... usually late July /early August, then I get a nice Fall bloom.

Yup. In my Cali zone I shear to ground in early spring...and you're even warmer than me.
Early spring is also a good time to divide this plant. Division is easily done with a shovel. Any parts you divide off the mother plant usually grow on their own quite well.

same here, major cutback in early spring and digging out any parts that I want to get rid of or give away. But for now I just let it do its leggy thing until it overly flops and irritates me, then I just remove the floppy part.