Without additional details on where those troops are (US or already on board ships in the Mediterranean?), it could mean a few things, but speaking from my own experience it would involve having all required equipment packed up and staged on a military base, personnel would have a bag packed and easily accessible, and any scheduled training exercises would likely be cancelled, especially if they were multi-day exercises. Normal daily routine would be the same. Any leave would be cancelled. 24 hours was how long we had to report to an assembly area for deployment, not necessarily actually leave the country, much less arrive at the destination.