論文アブストラクト：We propose the concept of "Situational When", an approach to understanding time in interface design not as a point on a calendar or clock, but as a set of converging circumstances that constitute "the time" for happenings to take place. Time is encoded both explicitly and implicitly in designed products. However, many technologies propagate business-centric, modernist values such as scheduling and efficiency, and marginalize broader socio-cultural aspects on which many activities are nonetheless contingent, e.g. the right people, the right weather conditions, and the right vibe. We derive our reflections from a case study of a cross-cultural digital noticeboard designed with an Australian Aboriginal community. Attention to the situational when opens up new possibilities for design that put greater emphasis on the social and relational aspects of time, the situational insights embodied in local narratives, and the tangible (e.g. people) and intangible (e.g. energy) circumstances that together make up the "right" time.