Noussair, C. and Stoop, J. (2014). Time as a medium of reward in three social preference experiments Experimental Economics, 18(3):442--456.

We use time, rather than money, as the salient component of subjects{\textquoteright} incentives in three workhorse experimental paradigms. The use of waiting time can be interpreted as a special type of real effort condition, in which it is particularly straightforward to achieve experimental control over incentives. The three experiments, commonly employed to study social preferences, are the dictator game, the ultimatum game and the trust game. All subjects in a session earn the same participation fee, but their choices affect the time at which they are permitted to leave the laboratory. Decisions that are associated with greater own payoff translate into the right to depart earlier. The modal proposal in both the dictator and ultimatum games is an equal split of the waiting time. In the trust game, there is substantial trust and reciprocity. Overall, social preferences are evident in time allocation decisions. We compare subjects{\textquoteright} decisions over time and money and find no significant differences in average decisions. The pattern of results suggests that results obtained in the laboratory with money as the medium of reward generalize to other reward media.