The attacks suffered by France in January and November 2015, and then in the course of 2016, especially the Nice attack, provoked intense online activity both during the events and in the months that followed. The digital traces left by this reactivity and reactions to events gave rise, from the very first days and even hours after the attacks, to a ‘real-time’ institutional archiving by the National Library of France (Bibliothèque nationale de France, BnF) and the National Audio-visual Institute (Institut national de l’audiovisuel, Ina). The results amount to millions of archived tweets and URLs. This article sets out to explore the creation and the temporalities of this ‘born-digital’ heritage. It seeks to highlight the most significant issues guiding initial research carried out on these relatively unedited corpora, from collection to exploitation, online stream of data to its mediation and re-composition.