
I am rather surprised your vet did not offer the Alizin injection (can be given up to 42 days after mating and normally after the season finishes so no chance of bitch being mated again that cycle) or even a gravid spay for your girl, problem sorted.
As for labout hwo long is a piece of string.
I have had bitches have their pups from 5 days before and 4 days past due date from first mating.
I have had bitches show little signs of labour and present a puppy almost right away and had one go 36 hours before producing puppies.
I have had al 5 pups born in little over an hour and had 4 hours between pups.
there is infinite variation and everything normal and things can go wrong even with little time between stages and pups.
do you have an experienced breeder friend who knows your bitch who can be with you. it is best that someone experienced is on hand at any whelping. Otherwise it's like having your best friend with no medical training attempting to deliver your baby.
Most vets unless breeders know little about whelping other than doing C sections so are of limited help.