my bitches water sac burst at 530 this evening,it is a first time for both of us,i have made the vet aware that she had started,however as yet no pups have arrived,she seems comfortable and has not started straining,how long is reasonable to leave her,it does not say how long in anything i have been told or read,although the book of the bitch says it should be fairly imminent after the sac breaking,thankyou

I would take her to the vets. I believe a pup should have been born by now. It may be stuck. Better safe than sorry.

About two hours is OK from the appearance of the water bag (which doesn't contain a puppy).

If nothing has happened by now, I would say get her to the vet IMMEDIATELY!

Good luck, let us know if everythings ok.