> I have also heard of other breeders stating their bitches, toy breeds, whelps every time on day 56 with pups being perfectly sized and viable.
It's not just Toy breeds, there are others, from what I have read.
And there's a reason for that - not that they don't need as long a gestation as others - they have exactly the same.. but other things can *appear* to give a shorter pregnancy.
There are two variables involved - Firstly the timing of the ovulation, which can be almost instantly afterwards, or even before the bitch is ready to stand. Or several days later (the sperm can stay alive for some time).
Then you have the timing of the implantation when the fertilised eggs take their place in the uterus and start forming properly. That again can vary.
I am used to breeding cats where the ovulation happens during mating or shortly afterwards (up to three days later, also varies). This means there is nowhere near the variation in gestation term seen in dogs - who will ovulate whether mated or not, and often some time before they are mated whether they stand or not.