The wall needs to be free of bows, twists or raised areas over approximately 2-3mm. Any sharp areas need to be removed. Any unevenness less than 2-3mm can be taken up by the adhesive. The walls will be obscured by the coloured/printed glass so the surface does not need to look pretty. Wiring must be chased into walls and any light fittings should be fitted allowing at least 10mm for the thickness of the glass and adhesive.
The silicone/adhesive can be applied using a silicone gun, putting small circles every 50mm on the back of the splashback.
Providing your splashback is supported by the worktop, just use masking tape to hold the splashback in position while the adhesive sets
It will change slightly for different adhesives, however, as a general rule - 24-48 hours (please read the instructions on the product you use)