My vet says 3/4 months after the bitches season. They are happy so long as its done between the two but wouldnt leave it over four months.
I don't know if its just coincidence but my friends bitch had a phantom, or was having a phantom and the trainer at our classes told my friend to put away all toys so that she would stop all the nesting instinct and that did seem to work and she hasn't had any problems since, all the symptoms stopped. My friend and I were never sure if it was because of the toys or not but the trainer is a very experienced, groomer, breeder, trainer and vet nurse.