The device will stay within Spiceworks indefinitely. You can manually remove it by using the duplicate (noun) option. That does not add the skip scanning entry in Settings > Network like ignore does.
And what, specifically, would you like to configure? If you're looking for a drop-off setting, you can always add that to the feature request forum. I think (not researched yet) that someone may have already asked that. Then again, I could just be going mental.