the average gestation period for a dog is 63 days. They can go up to 5days early, or 5 days late and still be ok. It is important to know exactly when breeding occurred.
In toy breeds especially, c-section are often needed. Once in full labor, I feel a bitch should not do hard pushing for more then 2hrs before seeking medical attention. Keep in mind your driving distance to your vet. I am 45 mins from my vets, so I would not allow my bitch to push more then 1 1/2hrs at the longest before driving to the emergency vet. Also I always recommend purchasing a large e-collar. That way if a pup is stuck, and you are driving by yourself, the bitch can not rip the sack open.
Good luck, and let me know if you have any more questions.
Now is the time to get a relationship with your vet. The mom needs vet check ups during the pregnancy anyway to ensure everything is going well. While there ask as many questions about whelping and puppies as you can.
You are going to need to read up on evrything from setting up a whelping spce to how to break sacs, tie cords, revive listless pups and when to call your vet.
Ask your vet what his normal business hours are. Let him know when your girls due dates are. Ask if he does emergency calls after hours, if not, get the phone numbers and directions to the ER vet that they reccomend now. Once trouble strikes its too late to try to save mom and pups if your not prepared.
Life isn't about waiting for the storm to pass. It is about learning to dance in the rain.