I think they just want to make sure, and double sure, that your phone is not on and wet. I have seen some people practically dip the phone into water and then apply the skin. I just lightly spray the skin and put it on. I got to the point that i stopped using those because the collected all sorts of dirt/grime on the sides, but I never waited a full 24 hours and all was always well.
"A dog is the only thing on earth that loves you more than you love yourself" - Josh Billings