When is the time right to mate my bitch?

When you have assured yourself that it is moral and right to do so and that she has something to offer the breeds gene pool.

and when she has been proved to be a good speciman of the breed,you are assured of her good temperament and you have found a suitable stud dog with the same attributes.
When you have enough money put aside in case of emergencies (eg ceaser)and when you can be sure that if any of the resulting puppies are in need of help during their lives (not just as puppies) that you have the neccessary facilities to take them back and rehome them....even if they are destructive or not house trained.
Oh...and when you can look at your bitch and say 'your possible resulting death is a risk I'm willing to take'...it DOES happen
Archer