No dumb questions, only dumb answers! 🙂
I would imagine as long as it's not left to sweat under tarpaulin, and your humidity is not through the roof, not very long at all.
So water won't get trapped under the tile when it is grouted? My concern is that it gets trapped under the tile, it gets grouted, than if we get a freeze in the winter it could crack and buckle.
There should be no gaps under the tile for water to get trapped in. The adhesive bed will have been rewet (like it was when mixed and used to fix the tiles) and it will again in the future as the grout will probably be water resistant but not water proof. I am assuming an appropriate outdoor cement based adhesive was used to fix the tiles to the substrate, then this should cope with the freeze thaw cycle providing it is a solid bed and that appropriate stress relieving movement joints have been incorporated (if it is a large enough area to warrant them).
