RE: will this hurt my air rifle?
10 to 15 mintues shouldn't hurt, but YES leaving a spring powered airgun cocked does weaken the spring. I don't leave any of my better spring guns cocked for extended times. There have been informal studies done showing that that leaving them cocked for extended periods is harmful. Several folks have chronographed guns before leaving them cocked then after leaving them cocked for extended time and found they had velocity lossed due to the springs taking a set. A pump-up gun probably wouldn't do anything but slowly leak off pressure.