Time has long been considered as an important dimension of the process of disclosure of information about genetic risk to kin. The question of the "right time to tell" has been frequently noticed but seldom placed at the centre of the analyses of social scientists. Based on an ethnographical fieldwork in a French cancer genetics clinic, this article aims to show that many dimensions of the practical issues of disclosure to family can be fruitfully addressed through the temporal lens of kairos. Relying on the case of hereditary breast and ovarian cancer risk, it firstly highlights the existence of a mismatch between the "chronological" time of prevention proposed by professionals and the "kairological" time of disclosure lived by informants. Secondly, it emphasizes the problematic nature of the pragmatic approach of time associated with kairos. On the one hand one can draw some benefits from seeking the right time to inform relatives, but on the other hand waiting on uncertain opportunities to disclose such information can make communication even more difficult.