My cats had kittens how long till I can spayed her as she want's to go outside.but now I've let her out what now..?

Cats go into a kitten heat anywhere from the day after to a few months after they give birth. If she gets pregnant while the babies are nursing, then she'll stop producing milk and reject the kittens in favor of preparing to raise the new litter.

Vets don't like to fix a female until her milk dies up, because there's a higher risk of complications. So, you should wait until the kittens are weaned before getting her fixed.