New Sump Pump Question

I've just today had a sump pump put in my basement. The install isn't finished yet, but the installer showed me how to test the pump. It's a Little Giant and he said to suck on the tube on the end of the cord. When I checked the sump a little while after he left, the water level was several inches above the pump, but it hadn't turned on. I then did what he said and sucked on the tube and plugged it back in. The pump worked great, but it wouldn't turn off. I let it run for a good 30 seconds after the sump was empty, but it didn't stop. I was worried that leaving it go would burn out the pump. My question is, how long should the pump run for after the sump is mostly empty and not pumping water anymore? The installers are going to be here tomorrow, but rather than bother them for something that might be really stupid, I figured I'd here here first. Thanks!