Cakes with whipped cream frosting should be stored in the refrigerator. But if you keep it out for a while (to display, to warm up before serving), no harm. Just be sure to refrigerate any leftovers as soon as possible. And keep it covered when in the fridge; whipped cream can easily pick up odors from other things in the fridge.
Hope this helps, and hope you stick around here! eace:
Depending on the other ingredients , powdered non-dairy creamer mixed with a bit of hot water then left to cool can be a sub. for cream and milk that will keep in a cool place (and well covered) in the kitchen for up to 3 days. I do this for cakes being covered with decos and fondant and such for weddings and other special occasions. Before deciding to leave out, however, look at all the other ingredients...fruit especially is perishable when left out. If you choose this route...buy the brand name product. You can also get a bit creative...creamer comes in lots of flavors!