Different drugs work differently on each person, whose brain chemistry is sensitive to the kind of drug she's on. Though I'm not on Risperdal, I can tell you that when my pdoc instituted a cross-titer from the Stelazine to the Geodon [and then went higher on the G by 40 mg] it took two years to get the maximum effect. Added to that, not all drugs relieve all symptoms at all times, so sometimes I have a minor flutter here and there. My psychiatrist believes total symptom relief is the only acceptable outcome, and I agree with him when he set this goal for my treatment.
I would say six months is too early to definitively answer whether you've found the full relief, and by three years you should know if things are adequate. Even better, a person can notice gradual, improved shifts towards symptom relief throughout the course of her recovery.