While it's acceptable to compress a sleeping bag during travel or a camping trip, it's not recommended to store a sleeping bag in its compressed state for extended periods. Keeping a sleeping bag compressed for long durations can damage its insulation and reduce its ability to trap heat effectively. Ideally, a sleeping bag should only be compressed during transportation or when being used on a trip. Once you're done with the trip or you've reached your destination, it's better to unpack it as soon as possible. When storing your sleeping bag for more than a few days, the best practice is to keep it clean, dry, loosely packed or hung up in a cool, dry, and dark place. There's no definitive timeline for how long a sleeping bag can stay compressed without damage, as it greatly depends on the type and quality of the bag's insulation. However, minimizing the time spent compressed will help maintain its loft and warmth for a longer time.