Can stroke or seizure from ritalin (methylphenidate) cause permanent damage? how long after would damage be seen?

YES: For stroke: acute damage presents either immediately or shortly thereafter. Damage would depend on the extend and damage caused by the stroke. Sometimes treatment (med ; occup therapy) can mitigate longterm damage. With seizure, usually no longterm damage (unless injury during seizure), but repeated generalized seizures can alter cognition.