Hi Mal, yes you can add a time switch, the easiest way is to take out the flex going from switch to immersion, put in a new piece of heat resisting flex from switch and connecting both into an immersion time switch, but obviously the switch will have to be left in the on position permanently, and I know it is obvious, but remember to turn power off first, the reason i suggest doing it that way is, that if a problem does occur on immeresion it is easy to isolate the supply, good luck, Ray