Contrary to what Jack Flash wrote, spring life is rated by number of cycles rather than compression time. In other words, they will start to fatigue after a certain amount of use. Time spent compressed is almost irrelevant.
My buddy bought a 1911 from a widow which had been stored along with 2 fully loaded magazines in her attic since her late husband returned from WWII. Those magazines had been fully loaded for over 50 years!!
We took the gun out and inserted a magazine, chambered a round and squeezed the trigger. BOOM! It worked perfectly and chambered the next round.
Both magazines worked fine until the very last round, which they both failed to chamber. Not bad for springs kept compressed for over 50 years.