hi i am making a cross cupcake cake later on today for my neices baptizm tomorrow. i am filling them with ganache topping with american buttercrem my plan was to fill the cupcakes make the buttercream afix the cupcake to the cake board with buttercream then frost them place them in the box and let them sit out overnight. will the ganach spoil?

Ganache will not spoil.  I do it ALL the time!