Increasingly, adult mentors in informal, media-rich settings, like libraries and museums, seek to integrate both learning and civic engagement opportunities for youth into designed programming. This article illustrates how youth open and sustain opportunities for civic engagement over the course of a six-month, youth-driven program--Metro: Building Blocks (MBB)--housed within a digital media learning lab in an urban public library. Analysis develops the concept of civic rhythms as a means to feel out the social and affective contours of civic engagement that emerge in MBB. To better understand the civic rhythms of MBB, analysis focuses specifically on three rhythmic elements: pulsation, reciprocation, and oscillation. The article concludes suggesting that future research develop principles for designing-in-time that assist researchers and mentors in attuning to the youth-driven rhythms that sustain informal, media-rich programs.