One reason for letting instruments acclimate to their environment before opening is that with gloss finishes they will craze when subject to rapid changes in temperature. This is much more likely to happen than a problem with the wood. Temperature and humidity will effect wood expansion and contraction and glue joints. The use of modern glues has pretty much eliminated the glue joint problem. It is always better to err on the side of caution than to be eager and sorry.
"The dulcimer sings a sweet song."