#1). With any of the "pump ups" the first problem is that by compressing the air you heat it and it starts to cool immediately. Some loss of pressure.
#2). As I recall the instructions with my Benjamin, you were supposed to put 2 or 3 pumps in to keep the seals in place. That would be almost 60 years ago.
Ergo, best to pump "almost" and put the last couple in just before you shoot. How good your seals are and how long it will take to bleed down? This is where the cheapest break action shines. It don't compress until you pull the trigger. And any lube on the pellet helps too. Then there is dipping them in nicotine from the garden store and letting it dry. If it penetrates, it poisons. Luck. Happy Trails.
The old 5MM Sheridan I inherited from a cousin was rebuilt a couple years ago. After testing it out for accuracy with a couple different pellets, I put a couple pumps in it and can tell by the way the forend is tight against the metal that it still has pressure in it. The Benjamin Marauder PCP which sets in the family room guarding the bird feeder last got pumped up a few weeks ago with no pressure loss showing on its pressure gauge. However, some pneumatics are not supposed to be stored pumped up because their seals are not designed for continuous pressure. I think that is a bad design.