My vet told me it should be exactly (not approximately)three months after the last day of the season. To wait any longer, the bitch might be starting the run up to the next season and could cause hormonal probs for the rest of her life and we all know what that like ! ! We took our bitch approximately three months after her frst season and as we could not guarantee when her season ended the vet strongly advised us to wait. Could be a coincidence but she has such a lovely temperament it is unbelievable.
Its very difficult to know exactly when they start or stop their seasons, but if you go for approximately three months after you know they have actually been in you won't be far out. It won't matter if they are 8 or 9 monthly bitches because provided you don't leave it till nearer six months after they will still be between seasons.
Also, when we raced greyhounds they had to be off the track for twelve weeks from the date of their season starting, to ensure they were not in milk from a phantom pregnancy which would usually be around nine or ten weeks after the season date.