Time Currency, current times.

On October 15th, 2009, time/bank will present a one-day exhibition of time-based currency prototypes at the Frieze Art Fair.
We have asked a group of artists, architects, writers, activists and designers to suggest what they think would be the best representation for the exchange of time between each other, and to design a symbolic currency that is backed by trust within a cultural community, rather than by gold or state authority.
Can this token of exchange be represented, and if so, how?
time/bank’s currency is issued in half-hour, one hour, six, twelve and twenty-four hour denominations. The prototypes presented at Frieze, have been designed / proposed by: