HOw long should you let backboard set before you install ceramic tiles?
Ideally, if tou can give it overnight for the thinset to set up under the boards, that would be best, but tile is set all the time right after the boards are placed. The seams should be covered with mesh tape and coated with modified thinset. We usually recommend to do this when setting the tile as the tape/thinset combo when done beforehand causes a small ridge which could become visible with smaller tile being used. If you do place the tape beforehand you want the thinset coating to dry so you are not constantly stepping on the drying thinset.