This essay considers the notion of a 'real-time city' from a temporal perspective. The essay is divided into three sections. The first section examines how smart city technologies seek to utilise real-time computation to transform urban management and governance and the pace, tempo and scheduling of everyday life. The second section considers how ICTs are transforming the nature of time with respect to smart cities. It sets out a set of related notions of real-time temporalities (network time, chronoscopic time, instantaneous time, timeless time, machine time, code/spacetime) and unpacks the nature of 'realtimeness' and the relational, contingent, and heterogeneous nature of real-times operating across smart city platforms and systems. The third section discusses the politics of adopting real-time technologies in urban management and the conduct of everyday life and sets out arguments for the maintenance of asynchronous cities and the adoption of an ethics of temporal dissonance. The conclusion argues that there is a need for philosophical, theoretical and empirical work to understand the realtimeness of smart cities and sets out a number of questions that might guide such research.