We coalgebraically define a unified semantics for systems with an emphasis on the notion of time. Such a semantics intends to formalize system that underly system engineering (i.e. the discipline focusing on the integration mastery of large industrial systems).Moreover, we give a formal meaning to another important aspect of systems engineering : system requirements, constraining the expected properties of a system. To express such requirements, we define a logic that extends μ-calculus to our coalgebraic definition of systems. We establish an important property of this logic: adequacy.