How about skin watches. Fluoro digital readout is transferred to the skin much the same way temporary tattoos from show bags are. Using a fixed molecular lattice the digital readout simply reorganises itself as the seconds count down. When it reaches the zero point (the total number of seconds encoded) it fades away, the molecular structure breaking down and will finally be removed with a shower. I'm thinking 100c for a 2 week skin watch.
This of course has all sorts of other interesting applications as well…
