How long does the tile have to dry before I can put it on the wall ? Should I dry it with a heat gun or is drying it with a towel good .
If you are using thin-set, then damp is fine (as in, dry with a towel). It is usually a good idea to damp the tile and substrate with a sponge anyway, (especially if tiling to wood/gypsum(drywall) etc.) so that the substrate doesn't soak up all the moisture from the thin-set.
If using mastic, you want the tiles to be dry.