DO NOT let the admissions committee or anyone in the admissions office know that you want to defer until you are officially affected. It might ruin your chances of getting in. I kinda made the mistake of doing that at one school (where i am wailisted), even though my intentions were sincere and more of an inquisitive type. But the lady told me it was best to wait to get accepted (which in case of this schools is probably going to be in the summer, if at all).