Depends- if its 2nd stage labour then witin 30 mins of hard labour ( pushing, panting, digging, looking uncomfortable) if 1st stage and contractions not strong nor frequent then can be as much as 24 hours before 2nd stage. Each pup should arrive within 30 mins of each other any longer and it could be stuck. We waited 2 hrs before getting to the vets( as they advised as she didn't appear to be in distress) and the stuck pup was dead and she almost had to have a caesarian. Luckily she didn't and was able to deliver normally at the vets with the help of several oxytocin injections to restart labour but had we waited not only was the pup dead but she may have been unwell and certainly too tired to birth vaginally and a caesarian is only option to save mum n pups . I hope your dog is ok and all puppies arrived healthy!! Best wishes