
The 'norm' (and yes bitches don't read the books) is usually between days 9 and 14 and usually when the discharge has gone to a light straw colour. I have never tested, but go by how both react when put together, especially if the male is a proven experienced stud dog. Using a maiden bitch to an unproven male can make things less 'obvious'. Most of mine tended to go by the book, but I had one whose discharge had gone light, and was bred twice, who then went back to a darker coloured discharge for some reason. She had an uneventful pregnancy and produce 9 of probably the best puppies we'd ever had.
This is what makes breeding a challenge