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.