These labels have been sitting on top of my hot tub cover for almost a year now and counting. I am in Tucson, Arizona and these labels were placed in an area where they receive most of the Arizona sun and have already survived their first summer. The top label has no lamination, so it did not fare so well. The bottom label has barely faded from the original look and shows little sign of wear. The UV lamination we use is very high quality and rated for many years of outdoor use.
These labels have been pretty much in the worst case scenario situation. Under normal circumstances, I would not even recommend placing any label horizontal on the top of a surface that sees daily sunlight exposure. They should be placed vertically on the side where they will see the least amount of sun, but as you can see, even if you have to break this rule, you will be ok for a while.