The rate of Change

Humans can change. That I acknowledge as fact. It does lead me to wonder though, is there a rate for this change? Is there a limit to how fast we can change, how fast we can become a new or different person? It is said that a man can't change overnight implying that change cannot be instantaneous. Is that true? What about a moment's decision that can change our entire life? Does this not qualify as instantaneous change? If we say that change is not instantaneous can we then set a minimum amount of time that is required in order for a person to change? If we cannot, then how can we rule out the possibility of instantaneous change? What do you think? Is it possible for a person to change in a moment or does it take longer than this? How long?