Instruments have been transported for decades tuned to pitch and brought from freezing cold greyhound luggage storage hoppers to the stage in under an hour. Did anyone worry back then or notice problems? Now we have shippers demanding instruments be de-tuned and manufacturers and retailers asking for a 24 hour waiting periods before opening. It's BS.
I would not be so quick to call this BS.
Several users within this thread, myself included, have given REAL examples of these types of issues happening, my own example less than a month ago (albeit with an acoustic guitar, but still). So yes, many people have noticed problems.
Just because you've personally never had a problem with this, does not mean that these problems have not occurred for others. On a similar note, just because things have generally been done a specific way for decades does not mean it is the 'right' way, 'best' way, or safest way. We can always learn as we go and adjust our approach/methods based on what we've learned and experienced. Neither of us has any data on which to base a claim about how often this did or did not occur with instruments over the last few decades, only our personal experiences. In my personal experience, it has actually happened to me, so it is not BS. I may have very well been in the same camp as your comment, until this
actually happened to me.
Regarding your comment about shippers/manufacturers/retailers requesting these wait periods now, can you blame them? It is probably a result of REAL LIFE CASES like mine, and others in this thread! Maybe they've learned over the last few decades that this CAN be a real risk, a risk that can potentially be mitigated somewhat by wait/acclimation periods, so it is advisable for a business owner to suggest these wait periods to customers. Otherwise, they are responsible for the damaged product, so this makes perfect sense to me.
For example--I guarantee the shop owner I got my acoustic from recently will now recommend this acclimation period in any future case where he feels the climate might be a concern! This is a great micro-example of how shippers/shop owners/manufacturers may have moved from not recommending this decades ago, to recommending this now. This shop owner did not recommend an acclimation period when I initially ordered the first guitar, but now that we've gone through this issue, he's adamantly recommending it with the replacement guitar. If a business owner had this issue happen with even ONE customer over the years, it would likely have made an impression, and would potentially spark the business owner to look for ways to avoid this moving forward. Hence the suggested wait periods when major climate change is a factor during shipment.
Of course, this is probably a low risk in general, and it certainly doesn't happen on a high percentage basis from my experience (and from what I've read). That said, for the percentage it does happen to, it REALLY sucks, so better safe than sorry. Of course, everyone is free to forego these suggestions and open the instrument right up if they'd like. Just know that for some people, this really has happened, and it is not fun whatsoever.
Just my $0.02.