Hi DJ,
Cool down period means the time it takes for the primary mirror to change to the same temperature as your surrounds. So i guess if you had your air conditioner set to cold in the house and took your scope outside it might need to warm up as well.
Hope this helps.
Look along a hot road and you can see it shimmer. Same sort of thing happens with optics. This is the best i can explain it,cause i'm a noob to,lol
Cheers,
Duncan
