I've made some molds out of half and half and having difficulty getting them to completely dry . will they always be a bit soft? Will putting them in buttercream alter them at all? Will the butter cream be enough to hold amll pieces to the sides of the cake or will i need to use royal icing?
Depending on the weather/humidity it might take longer to dry. I've had some pieces that take a couple days and some take a week or more to completely dry. It also depends on how big your piece is too.
The buttercream shouldn't change them, I have never had an issue. And buttercream should be fine to hold them in place.