When is it best to add decorative pieces to a cake?

I'm making my first, more detailed, fondant covered cake. I'm planning to bake and let the cakes cool over night. Then crumb coat the cakes and cover in fondant. I will be adding flowers and over decorative pieces to the cake (made out of fondant as well using silicone molds). Is there a best time to put these additional pieces on? Do I have to add them right after I cover in fondant or can I wait until the next day? If so, where should I store the cakes? On a cake I made a while ago I put he cake in the fridge for a few hours and the fondant began to crack. I'm using fondant I made if that matters.