I am planning on makin g a fourth of July cake, I already have the cakes made and filled with buttercream using crisco. I am wondering if it would be safe to cover them with fondant tomorrow night, to be served the next day. I am afraid the buttercream might seperate and start to ooze because of the heat. Any help appreciated!!

I'm no expert, but i would cover the cakes and put them somewhere cool, then cover as you need.