Models of ambiguity aversion have recently found many applications in dynamic settings. This paper shows that there is a strong interdependence between ambiguity aversion and the preferences for the timing of the resolution of uncertainty, as dened by the classic work of Kreps and Porteus (1978): the modeling choices that are being made in the domain of ambiguity aversion influence the set of modeling choices available in the domain of timing attitudes. The main result of the paper is that the only model of ambiguity aversion that exhibits indierence to timing is the maxmin expected utility of Gilboa and Schmeidler (1989). This paper also examines the structure of the timing nonindierence implied by the other commonly used models of ambiguity aversion. The interdependence of ambiguity and timing that this paper identies is of interest both conceptually and practically–especially for economists using these models in applications.