Functional Reactive Programming (FRP) enables a developer to describe, declaratively, a program’s response to external events. FRP has many implementations that share many common features, but lack a common declarative mechanism for describing time constraints, such as deadlines or rate throttling. We present a set of Metric Temporal Logic (MTL) primitives for expressing real-time relationships between events in a reactive system. Providing these primitives in the core of an FRP framework allows a developer to define new time-based constraints without resorting to timers external to the FRP code. We describe the implementation of the basic MTL operators in a modified version of the Sodium FRP framework and demonstrate its use for an implementation of the debounce primitive provided by the Java implementation of ReactiveX (RxJava).