Six days too close to cancel an interview?

Six days might still be far enough out for them to fill the interview slot. Obviously further out would have been better.

 

It probably won't adversely affect you to cancel now, but you should do it ASAP. Be sure you don't "need" the interview also.

 

of course, the earlier the better, but if you really don't want to go, you would spare i.e., two faculty members from this extra responsibility, plus save some travel money and get to sleep in an extra day.

 

You don't really spare the faculty -- a school will try to book up the slots with folks on waitlist or who call/email in because they haven't heard anything yet. If anything it makes it harder on the faculty because they may have already read up on your application, and now have to do that again for someone else.