You could make them in advance if you froze them, then decorate and let defrost. However, if they are not going to be frozen, they need to be made the same day IMO, or at the very earliest late the night before. Larger cakes last longer.
jetstar, i made some red velvet cupcakes for comic relief, made them early in the week as i wasnt sure what they'd turn out like, i froze them, again not sure if i could, didnt decorate them though, defrosted them night before and they were fab.
I am making 40 cupcakes for an event on a Sunday. We are having visitors the day before. So will the it be ok to bake the cakes on Thursday and ice with buttercream on Friday? Or should I really bake them Friday and ice Saturday? Not sure how long they will take to ice and decorate. TIA