The thickness of the tile or whether it is unglazed or glazed tile doesn't matter.
The manufacturers of the thin-set mortar adhesives typically require their products to be stored and used within certain temperature ranges. Typically it is between 40 degrees F and 90 degrees F.
That means that the setting materials, the tile, and the substrate can't exceed those temperatures during installation or storage. Humidity can be an issue too because high humidity will retard the curing of some materials. And wind can compound the problems in terms of causing lower or high temperatures and causing materials to dry too quick and possibly skin over losing its tackiness (ability to bond).
So if your customers are going to install an appropriate exterior tile considering slip resistance, and resistance to moisture and wear, then they have to monitor temperatures. There are a number of ways of doing that. We are doing a big outdoor job in Palm Springs right now where the temperatures are over 110 degrees F during the day, so the tile is being installed at night. Even then temperatures can exceed 90 degrees F at night, so the installers will put ice in buckets of water and wash down surfaces before installing. Often shading will suffice during the day light hours by putting up shading clothes to reduce temperatures, which can reduce them by 15 degrees or more. You can tent areas and have air exchangers and misters working to keep the temperatures down.
So it is important that manufacturers' data sheets are followed if your clients want the products to perform as they should and if they want to maintain the manufacturer's warranty.
Our University of Ceramic Tile and Stone campus at www.UofCTS.org does have several online training courses teaching the basics about ceramic and glass tile, natural stone, and for tile installations.