Question about gum paste flowers?

I just made some gum paste roses and I was wondering when I could put them on the cake. Can I put them on before they are completely dry or do I have to wait? The cake is supposed to be deliverd Sunday. This is the first time I have worked with gum paste, so I know very little about it. I just made the flowers and put them in a airtight container. Or should I leave them out? Also I used the Wilton Gum Paste Mix powder. Oh and should I freeze the leftover powder or is it okay on the shelf. Thanks in advance.