I have a little more time now. mikee, ideally, the best time for breeding is AFTER the dogs are fully mature, physically and mentally, AFTER they have been graded by professionals as worthy breeding animals, AFTER they have been fully health tested (for hip and elbow dysplasia, von Willebrand's disease, thyroid panel, eye defects, liver and kidney panels, cardiac ultrasound and Holter monitor ecg along with the DNA test for dilated cardiomyopathy, and brucellosis), and AFTER you've extensively studied the pedigrees of the dogs to determine if they're really the right match for one another and to learn the ages/causes of death of their ancestors so you know what kinds of problems they are carrying. Make no mistake, they ARE carrying problems. It's up to you to know what they are, and how to minimize them.
Beyond that, the best time to breed is AFTER you've fully learned what breeding is all about and what it really entails. It's much more than just knowing when to do it.
Obviously, one can cut all of those corners and do nothing listed above. But then they are classified as backyard breeders (in other words, ignorant and/or irresponsible breeders).