This work proposes a fundamental reformulation of time, not as a pre-existing geometricdimension, but as a localized and emergent reaction of the quantum vacuum to the presenceof mass-energy. We argue that time arises only where and when the vacuum is causallyand entropically disturbed by matter, and is otherwise undefined. A scalar field χ(x) isintroduced to represent the degree of temporal activation in spacetime, governed by a fieldequation sourced by the trace of the energy-momentum tensor. This framework offers acoherent reinterpretation of relativistic time dilation, entropy-driven temporal asymmetry,and the quantum nature of vacuum. It provides a physically grounded mechanism for theemergence of time during cosmogenesis and resolves classical paradoxes such as the initialsingularity and the horizon problem. We discuss experimental predictions and proposeobservable consequences in atomic clocks, black hole interiors, and cosmic microwave backgroundsignatures. Ultimately, the model shifts the paradigm from asking "What is time?"to "Where and under what conditions does time emerge?"