Orchard RTR is a type of fondant icing which is sometimes known as "plastic" icing due to its smooth texture when it is rolled out. As Wonder has said, fondant covered cakes shouldn't be kept in the fridge, as they will sweat and go soft. They also don't like to be kept in a room with an evaporative airconditioner for the same reason. They should be kept in a box or a container that is not airtight.
Fondant on cakes will keep for months- just think about the traditional fondant covered fruit cakes for weddings or Christmas cakes. It is the cake underneath and any buttercream/fondant under the fondant that determines how long the cakes will last. Obviously, butter cakes and the like will only keep fresh for a couple of days, so choose a cake recipe that you know will keep well for a couple of days. Once the cake is iced, the cake is no longer exposed to air and will keep better than an uniced cake.
If you bake and ice the cakes in Friday, use buttercream instead of ganache under the fondant and store in a cool room in a box, the cakes should be fine for Sunday.
Good luck, and post some photos for us
