How far along is my cat?

I've taken in a cat six weeks ago that didn't look pregnant then at all, but does now. It hasn't been back outside since. I wonder how long I've got to get her a good place ready to have her kittens. How long do cats remain "un-pregnant-looking" at first? I hear gestation is about 64 days. How many of the first days are unobvious? I suppose I still have about two weeks, but do I?