Is it normal for a cat to be in labor for more than 6 hours?

I noticed today shortly after 4:00PM That my pregnant cat, Raven. Has the amniotic sac sticking out. She hasnt been pushing much. She gets very restless and insists that someone is always near her. She hasn't had any kittens yet. I am extremely worried about her. She has had kittens before. and it never took this long. I'm scared for her. Is everything normal am i just over reacting or could something be wrong? Please help I love my kitty :(