Increasingly the material research deals with is cast as data. This is an ambiguous concept, which describes the matter of research in all stages of the research process. From having been seen as a stepping-stone on the way to producing the scientific results, increasingly data is itself positioned as the result. At the same time demands for data preservation and open data are often motivated with the hope that they will be of some use for new discoveries in the future. This poster highlights some of the ways in which notions of data emerge in the construction of big science facilities in order to raise some issues concerning implications for how and when knowledge production is thought to occur. We studied data and their making in setting up of two large-scale research facilities in southern Sweden, ESS and MAX IV, specifically of the necessary infrastructure for dealing with research data management. The main focus is on temporal aspects of data, thus shifting the interest from the question “what are data?” to the often more productive question “when are data?”. This also works to emphasis various sociomaterial entanglements shaping research data and its meaning in different organisational contexts.