She may not give you much warning beforehand at all. I remember when Abby was pregnant with Thomas and Cooper.....I knew that it was supposed to be soon....but she wasn't doing anything that I thought she would. She never "nested"....never decided on a place at all. She really never acted any different at all until she started labor.
I remember my daughter calling me at work and she was flipping out. She said, "Mom...Abby is crying and something is hanging out of her butt and she keeps trying to climb up into the computer chair with me!"
I think Abby must have been as freaked out as my daughter because she didn't appear to know what was happening. I got my daughters (both of them) to fix Abby a bed in my room and try to keep her there to have her babies. They had to sit by her side the entire time because otherwise, Abby tried to follow them.
I got home from work about two hours later and she had just finished giving birth to Cooper. (Thomas was the first born) So I didn't get to see them being born. But then she went into labor again 24 hours later, while I was home.....but that kitten didn't survive. The last kitten was a girl and looked exactly like Cooper. I was extremely sad that she didn't make it.
Just be prepared.....it could be anytime and you may not know when it's going to happen. Best of luck to you all! Let us know how everything turns out and be sure to take plenty of pictures so we can see the babies!