The worst part is leaving them out in the sun, the rubber on Drag slicks is not UV protected and will derogate quickly if left in the sun. It would not hurt to leave them on the ground, if they have the enough air in them, just put them on something nice and smooth, not rough gravel and cover them up from direct sunlight.
Drag slicks are usually only good for so long after the first burn out, this a common part of why people get lost on a tune up, or set up. Thinking that slicks last forever. In the spring get a new pair of shoes ,