I want it to still taste scrummy, but am a little short of time the day or two before the weekend, how long will it last?
My friend does this every year (mansions, cathedrals, and castles). She makes everything from scratch and likes to make them the day of the party. It will stay upright for a week or longer if the house is not too humid (including humidity in the air and the frosting/decorations that touch the gingerbread) and that no one eats any supporting structures prior to the party. :)
It depends on what you are using for the "walls" and the "mortar". "Mortar" made of powdered egg white plus cream of tartar becomes really stiff and provides a lot of structural stability. Cake-like gingerbread won't hold up well at all. After some years, I switched to graham cracker walls and put more attention into the decoration, as that's what mattered most. CAUTION: certain common household pests love things like this, so work out beforehand issues of whether it will be kept for decoration.