Irene,
I have read that hard labor can go on for hrs. before a puppy even appears, and I have not even delivered my first litter yet, so I can't really talk, but this is an article that was sent to me in order to become more knowledgeable about breeding. Nothing meant by it, just good info I thought.
Hugs.., Karin
http://www.thedogplace.com/library/rx.htm