Well, as Anuire pretty much conquered most of Cerilia (except Vosgaard) very early on, around 50 HC I believe, then I've always assumed that the colonisation of Aduria took place shortly after this. However, Rich Baker's Aduria material suggests that the westward expansion of the Empire took place around 800-900 HC, i.e. during the height of the Anuirean empire.

It may be that some regions (Mieres and the Gold Coast) were settled earlier, while other lands took longer to be subdued.