This has been covered before, somewhere here.
Springs "go bad" only from being flexed, not from staying in one condition or the other.
So you can leave a magazine fully (or partly) loaded from now until the end of the world, with no bad effects to the spring.
However, every time you unload a magazine, and every time you reload a magazine, you are flexing its spring.
Repeated flexing fatigues the spring's metal, and someday it will fail.
Rotate your magazines, giving all of them equal use.
(But it's OK to leave a couple of them fully loaded, forever.)