Deterministic models play a crucial role in computer system development, enabling the simulation and verification of system behaviors before Model-Driven Development (MDD) tools transform and compile these models into final implementations. Ensuring determinism is essential to guarantee that the behaviors of the implemented system maintain the properties analyzed in the models. This paper investigates the semantics of deterministic models for data-flow networks, where systems consist of components that compute functions on streams. While Kahn Process Networks (KPN) serve as a well-established semantic theory for time-insensitive deterministic systems, it proves inadequate for systems with time dependent components. To address this limitation, we use the concept of timed streams and develop a fixed-point theory tailored for time-sensitive systems in the style of KPN. This theory serves as the foundation for the MDD tool-chain, known as MIMOS, currently under development in Uppsala.