The fulfillment of time requirements is one of the major acceptance criteria of safety-critical and real-time systems. They are dictated by the environment of these systems and are often well known at the early phases of the development process. At the same time, the time behavior is a cross-cutting concern, not bordered by the behavioral design units, e.g. components or classes.

This paper argues for consideration of the time behavior as an explicit model-based view on the system under development. It proposes a modeling language and an analysis method. The formal graphical modeling language allows the explicit notation of time requirements and the integration with the architectural and behavioral aspects of the system. The analysis method allows the developer to verify requirements in respect of their consistency and completeness as well as to validate design concerning the fulfillment of time requirements. It supports modular development, for which results are presented.