How long does it take (roughly) to rebuild the beneficial bacteria after a week's course or antibiotics?
As with treating anything there is never any specific time as there are just to many variables such as how was the flora status prior to the antibiotics, how strong were the antibiotics, what are they using to rebuild their flora, etc.
In general though it should not take very long if done properly, which means using live probiotics with as wide of a variety of flora as possible and prebiotic sources to feed these flora and the original flora that survived the antibiotics to reestablish their growth.