Last year I took a study/vacation month in July to get CK out of the way, but I wasn't able to schedule CS until February. Other than the occasional comment from an interviewer that my step scores made it clear that my academic skillz were more than good enough, no one really mentioned the exams in the interview process.
I had also heard the rumor that some schools were beginning to require CK scores to either offer interviews, or, more commonly, rank an applicant; since my CK score was already in by the time applications went out, the point was moot and I never found out which schools these were...sorry I couldn't be more helpful in that regard. I would definitely email/call the program coordinators of any programs you are particularly interested in to ask about their requirements if you're worried about it.