Microfluidic interfacial tensiometry was developed recently, and applied to simple fluids and their mixtures. Here we exploit microfluidics' inherent relationship between time and space to demonstrate its ability to measure time dependence of the interfacial tension of a dilute aqueous solution of butanol in oil (the latter being either canola or silicone oil). Butanol is surface active and reduces the interfacial tension. However, as time passes, butanol transfers to the oil phase, where it is more soluble, causing a decrease in its interfacial concentration, and a rising interfacial tension. The kinetics of this process on the time scale of approximately one second is here measured and modeled effectively.