Recent research at the cross between cognitive and social sci-ences is investigating the cognitive mechanisms behind coop-erative decisions. One debated question is whether cooperativedecisions are made faster than non-cooperative ones. Yet em-pirical evidence is still mixed. In this paper we explore theimplications of individual heterogeneity in social value orien-tation for the effect of response time on cooperation. We con-duct a meta-analysis of available experimental studies (n=8;treatments=16; 5,232 subjects). We report two main results:(i) the relation between response time and cooperation is mod-erated by social value orientation, such that it is positive forindividualist subjects and negative for prosocial subjects; (ii)the relation between response time and cooperation is partlymediated by extremity of choice. These results suggest thathighly prosocial subjects are fast to cooperate, highly individ-ualist subjects are fast to defect, and subjects with weaker pref-erences make slower and less extreme decisions. We explainthese results in terms of decision-conflict theory.