Welcome to Pet Talk, but it really breaks my heart to know you let your cat get pregnant on purpose. The average gestation for a cat's pregnancy is 63 days. I do extensive rescuing of abandoned cats and kittens, and there's just not enough homes available to adopt all these unwanted kittens. Please, PLEASE get your mom cat to be spayed, and find responsible homes for the babies where they'll be spayed and neutered to prevent future litters.
And please click on these links....

http://st15.startlogic.com/~justonel/accidental.html

http://www.itsmeowornever.org/homeless.html