Abstract This article explores the closely knit yet complex link between proscription and temporality through the examination of terrorism trials in Nigeria. Through the notion of proscribing time, this article demonstrates the ways in which proscription is enacted, imagined, and contested in light of important temporal effects. With a few exceptions, recent debates around proscription remain almost overwhelmingly focused on the banning of particular groups linked to terrorism, and on proscription power and its wider political and ethical ramifications. This “actor-oriented” focus (proscribed/proscriber), I argue, reinforces certain theoretical and ontological claims recognizable in the dominant analysis of terrorism. Moreover, such a perspective is predominantly organized around a forward-oriented logic of security preemption, which does not fully reveal the complexity and broader consequences of proscription. Thus, drawing upon relevant insights about temporality, especially as discussed in critical security studies, critical legal studies, and beyond, this article demonstrates how time is proscribed (rather than terrorist groups) to render visible the complexity and ramifications of proscription. The article, as such, contributes theoretically to ongoing debates about proscription and temporality in critical security studies more broadly. It also, empirically, makes a worthwhile contribution to a relatively small, though important, scholarship on terrorism trials in Nigeria.