I get so jittery and nervous right before i make a cake and i worry about all these little details!!!

I purchased sugar diamonds for a christening cake i have to make this weekend. the label says moisture and water will cause the diamonds to turn white. The cake must be refrigerated until right before serving as it will have a cream filling. Should i put the diamonds on at the restaurant as opposed to the time of decorating where the cake may get moist from coming out of the refrigerator and to the place (it is warm and a bit humid)? or will it be ok if i put it on from the point of decorating? Has anyone ever used them before?