Don't let them sit, that won't break the springs in. SHOOT IT! If you're having trouble racking the slide, you might be trying to sling-shot it instead of using an overhand grip. Two fingers at the back of the slide isn't as strong as all your fingers and the palm of your hand on the slide. Worst case, lock the slide back and insert the magazine, then use the overhand grip to release the slide into battery - problem solved. But SHOOT IT!
If you can't shoot it, then cycle rounds through the magazine. By this I mean load the magazines, dump the rounds back out, and re-load the magazines. Lather, rinse, repeat.
Springs get "broken in" or "worn out" by the compression cycle, not from just sitting there compressed.
Edit to add: Keep in mind, the 10 rd magazine for the G30 is a 9rd with a baseplate extension. The 9rd is more concealable, the 10rd more shootable. You really should be using the Glock magazine loader in either case.
Regards,
Brian in CA