We are not aware of the exact time of the reappearance of the Imam (a.s); on the contrary he is hidden from us, till Almighty Allah accords him permission to reappear.
وأما وقت خروجه عليه السلام فليس بمعلوم لنا على وجه التفصيل، بل هو مغيب عنا إلى أن يأذن الله بالفرج.
Similar narrations
Kitāb al-Ghayba #680“One who fixes the time of reappearance for you, do not pay attention to his falsification, because we have not specified its time for...
Kitāb al-Ghayba #683the Imam (a.s): “Is there a fixed time for reappearance; so that we can sit quietly till that time?” He replied: “It was fixed; but you...