Hi! I am doing a cake for Friday (today is Wednesday) and I need to put a layer of chocolate mousse on top of the cake (not sealed inside) then top that with a swirl of buttercream (coffee cup cake and the mousse is the "coffee") Question: How soon can I put "unsealed mousse on the cake? I am afraid if I do it and refrigerate the mousse will develop a "skin". Thoughts or experiences?? Thanks all and happy decorating!