The revelation that they’re an imposter is instant; but there’s no reason the full reversion can’t take a little longer. In 5E D&D, Lycanthropes are immune to slashing, bludgeoning, and piercing damage from non-magical, non-silver weapons. How did people mistake shifters for lycanthro...
That depends on the origin you chose for them. If you follow the idea of an Overlord, than the curse would exist during the Empire. However, I think it would be extremely rare. Consider a) the Dhakaani are highly civilized and city based, and b) the Dhakaani were a highly regimented...