How long is it before their give brith to the kittens?

Please provide me with more context! I need to know who "they" are in order to answer your question.

For example:

* "How long is it before the cat gives birth to the kittens?"

* "How long is it before the pregnant mother cat gives birth to the kittens?"

Once you tell me who you're referring to, I can tell you how long it is before they give birth to the kittens!