It should hold air unless the tank or marker has a leak of somewhere. I always pressure drop test my builds overnight to see if there are any internal or external leaks. All my tanks hold full pressure in storage for for months, bar one that has a slight leak from the fill nipple. That's a 0.8L bottle only used on pumps so not an issue in play. A slight leak from a hose fitting is enough to empty a tank if left on the marker for a few days.