Q: After what period of time without seizure can a person be regarded as controlled?
A: It really depends on what you mean by "control."
For legal purposes, i.e., driving privileges, most states require that a person be seizure free for at least 6 or 12 mos, depending on the state.
If you mean a point where a person can be assured that seizures will never recur, either on or off medications, the answer is probably never, since breakthrough seizures can occur even decades after the last one.
For practical purposes, most epileptologists would consider 1 yr of being seizure free to be "good control," and some would consider medication withdrawal after two years of being seizure free. However, most adults with epilepsy do not successfully come off of all medications and do require some therapy to remain seizure free.