no one has any idea. i dont know and neither does anyone else whether it will ever go back to normal or how long it would take if it did.
if you sustained damage to the eye or nerves to the eye, then it is possible that it will never go back. if the pupil size difference is from the iritis or a side effect of the pred, then hopefully it will go back to normal.
as for the amount of time, no one knows. days/weeks/months/years/never...no one knows. too many factors to try and predict.