When to use campden tablets

[S.R.S]

I know there are many different posts on the above but I am still unclear when to add tablets to the water if brewing from a kit.
Should they be added 24hrs. from when you start making up the kit, in which case, some of the water to which the tables have been added will be boiled before adding to the wort, is this correct?
Any pointers appreciated, thanks

 

[Banbeer]

Just add half a tablet to the water the night before you intend making the kit and give it a stir.