Perhaps, but -- if I may make a comparison, imagine just now your shoulder started to itch. Would it not take a few seconds for you to decide you needed to scratch it? To the old gods, this is much the same. All this happened a terribly, terribly short time ago.

Of course, they should never have allowed their perceptions of time to become so shifted in the first place. [Gentle as she is, on this point Celestia speaks with absolute authority. She is qualified to chastise if anypony is.]