Condensation forms on the fondant when the inside of the cake is much colder then the outside. If you put it in the fridge at all it sounds like you will only need to do it long enough for the buttercream to chill and firm up but not long enough for the cake or filling to get cold. Hopefully that will help! If it does gather condensation again just let it sit (in front of a fan might be best) and let the cake dry and reach room temp. Just don’t touch it until it drys completely or you can leave fingerprints!