There are three stages of labor in dogs. The first stage is when the cervix is dialating and some contractions will start. You may see some shivering, panting, restlessness, unwillingness to eat and she may seek a private area. This stage usually lasts 6-12 hours, if you see these signs encourage her to go to the whelping area you have provided for her. Stages two and three are active labor and placenta expulsion. If she has more than one puppy she will alternate between stages two and three. Once she begins straining then you do not want her to go more than one hour without producing a puppy, if this happens it is a sign to call your veterinarian. Many dogs will rest between puppies for an hour or so, this does not require intervention but should you see active straining and no production then it might be wise to make a call to your veterinarian. But for the stage she seems to be in now depending on when it started you are looking at between 6-12 hours.