...should I use something else? I want to make a harry potter owl wizard cake, something like this- http://cakecentral.com/gallery/1907258 I want to make it relatively small and am wondering what I should make the owl out of? if I use RKT, how early can I make it? or would I be better using fondant/gumpaste?
You could either make it out of RKTs or out of modeling chocolate. You could make either one of those quite far in advance, even several weeks. Of course, if you make it from RKTs you would have to cover it in fondant or gumpaste or a mixture of the two. Let us know how it turns out!