Abstract
In this paper I present a problem for the conventionalist regarding temporal metrics, and I defend an objectivist position on the ground of its explanatory force. Roughly, the conventionalist has it that there is no fact of the matter with respect to the truth or falsity of judgments of the kind “event e1 lasted as long as event e2”, while the objectivist thinks that they are grounded in objective features of space-time. I argue that, by positing grounds for judgments of relative temporal length, the objectivist gains an explanatory force that the conventionalist position lacks.