I did not know either but it took my dog exactly 60 days. She concieved on February 14 th, and today is 4/14 it she just gave birth. I thought it was 3 months also, but I guess not. 60 days.
If you're asking about how long the gestational period is, it's 63 days, give or take a few. If you're asking how long a dog is in labour for, it can take several hours for pups to be born.
I have had three dogs and so far it took them each 3 months from the day they conceived to give birth.
my dog just had puppies and it took approx 63 days