So-called temporary uses of urban space, including 'pop ups' or meanwhile spaces, have recently attracted much attention by urban professionals as providing short-term 'solutions' to the 'problem' of vacancy. Yet the ways in which these urban innovations are conceived, studied and evaluated continue to reify a capitalist framework of development and conceptual understanding of the city that valorises exchange value and permanence. The result is that little empirical research exists about smaller projects that offer the city and its residents many non-monetary benefits. In this article, we argue that evaluating urban space according to the dichotomy of permanent or temporary land use is problematic: it misses the fluidity and multiple rhythms of how places are made and spaces experienced that are inherent to the regular life of any city. Rather than temporary use, we use the concept of 'interim space' to consider projects that may be responsive to local needs and available resources. Such initiatives often include 'non-visible' advantages which stem from use values, healthy place-making and creating shared spaces, offer alternative economies, and provide residents and guests with new ways of imagining their neighbourhood and city. To make our arguments, we analyse Granby Park, a 'pop up' park in north Dublin, initiated by the artistic collective Upstart that was open to the public in the summer of 2013, using qualitative research conducted before, during and after the official time the park was open. To begin a conversation about new frameworks of analysis that might capture the intricacies of interim urban spaces such as Granby Park, we conclude by offering a new concept, the 'improvisional city', to encourage more empirical research that takes seriously the many tangible and intangible benefits of these initiatives.