I have an event I am attending in about a week and a half.  I am taking several "demo" cakes with buttercream icing/decorations.  These cakes will not be eaten I just need them to look good but I am using real cakes not the dummy tiers.  How far in advance can I make?  Thanks!  

I would relax the rules maybe by a day or so -- I mean you could go longer too -- but i'm a firm believer in freaking out and over thinking stuff like this -- being over cautious -- I mean you could go even two days in advance of the usual routine -- are you using pound cake?

I made many many b'cream demo cakes as much as a week ahead.  Overbake the cakes so they are on the dry side and won't get moldy as fast. 

I'm just curious - if they are not being eaten then why not use the dummy tiers?