Scholars have identified several temporal challenges in foreign policymaking, such as variable time horizons and maintaining commitment or resolve over time. While the behavioural turn has emphasised leaders and their subjective perceptions, research often relies on rationalist conceptions of objective and linear time and struggles to assess leaders’ subjective perceptions of it. This paper theorises time as an intrinsic aspect of narrative reasoning in foreign policy, introducing a ‘temporal definition of the situation’ (TDoS) framework to capture leaders’ situation-specific subjective time perceptions. I then operationalise the TDoS framework’s key temporal features and show how it can be empirically examined. The value of the TDoS is illustrated by assessing the temporal perceptions of Bush and Obama regarding Iran’s nuclear programme, showing how their distinct definitions of the foreign policy situation shaped their subjective time perceptions and their corresponding responses. I conclude by discussing how this advancement can enhance behavioural research, provide insights into the ‘why now?’ questions surrounding leaders’ actions, and challenge existing understandings of time’s impact on foreign policymaking.