The belief that technology can be profitably employed to control and manage time has a long history. In this article we show how electronic calendaring systems have become emblematic of the contemporary vision of mastering time, codifying a distinctive quantitative orientation to time. Drawing on interviews with calendar designers at four prominent software development companies, we explore the quest among knowledge workers in Silicon Valley to embed a culture of temporal optimization through the use of calendaring software. Their collective response to this issue reveals that there is a specific kind of technoscientific world being developed: one fixated with solving the problem of time scarcity in contexts organized around maximizing prod...