The labels on these dry packs specify the floor life (in factory conditions: <30 °C and <65% relative humidity) for the device from the time when it is removed from the bag. You can find more information about handling moisture-sensitive devices in Application Note 71: Guidelines for Handling J-Lead, QFP & BGA packages.
Altera ships its moisture-sensitive packages in dry packs in order to protect the devices from any moisture-related risks. Damage may occur when a plastic device that has absorbed moisture is subject to the high heat from the reflow soldering process.