I am not 100% on this being correct, but I briefly remember a Psychiatrist saying that the patient has to be seizure free for 6 months minimum and preferred to have no seizure within the last 3 years to be asymptomatic. Do with that information what you will. but for Boards: 3 years.

This varies among states but in most of the states a 1-2 year free seizure period is required for epileptic patients to get their license