Relationship timing can have dramatic effects on diffusion through a network, as relationship order determines transmission routes. Though past research has modeled diffusion through static networks or developed methods for modeling change in network patterns, none has combined these factors to show how relationship change channels diffusion. This article formalizes the diffusion problem in networks with changing relations, identifies minimal bounds needed to measure diffusion potential in such networks, and provides a method for identifying who is at risk for diffusion. The effect of timing for diffusion potential is demonstrated with potential flow of sexually transmitted diseases (STDs) in an adolescent romantic network.