Anticipatory infrastructures assemble sensors that are ready to detect, networks primed to share data, scientists prepared to confirm events, and news organizations poised to tell stories. This article explains how public time is articulated through sensor-mediated communications by examining two anticipatory infrastructures. Each infrastructure uses similar earthquake data to detect, report on, and convene material publics around earthquakes in Southern California. They are integral to structuring rhythms, coordinating syncronizations, setting deadlines, and making events timely, meaningful, and actionable, yet their governance lives in no one place. Instead, they emerge from an assemblage of sensors, networks, devices, algorithms, people, data, organizations, professional practices, and normative theories of the public. By comparing two different anticipatory infrastructures, we show how imagined publics, forms of journalistic storytelling, representations of earthquake events, and system maintenance can convene different public temporalities. We identify four dynamics involved in making these variable temporalities in material publics: how human-machine relations organize time, how professional norms of timeliness collide, how publics are anticipated by infrastructures, and how sensor infrastructures are maintained or decay over time.