I know that people can start to feel sort of desperate because they are so nervous about this exam so I am going to humor you. I believe the consensus would be that you should only change your exam date based on whether or not you feel prepared enough to score high enough to meet your expectations. If you do not, then by all means change the date but do not base this on anything else other than what affects your ability to perform. Quit worrying about the alignment of the stars and study!! Blessings.