One thing I was told about CS was you need to take it early enough so that if you fail, you have time to re-take it before you graduate. My school made us do it before december. I'm not a PD, but I really don't think they care since almost everyone passes, and it is pass fail. It's not like rocking CS helps your application.
CK is different. If you think you'll improve your score over step 1 you might as well take it before november. If you think you are going to get a similar or lower score you should wait till later in the season.