We propose a compositional modeling framework for Mixed Reality (MR) software architectures in order to express, simulate and validate formally the time depending properties of such systems. Our approach is first based on a functional decomposition of such systems into generic components. The obtained elements as well as their typical interactions give rise to generic representations in terms of timed automata. A whole application is then obtained as a composition of such defined components. To ease writing specifications, we propose a textual language (named MIRELA: MIxed REality LAnguage) along with the corresponding compilation tools. The generated output contains timed automata in UPPAAL format for simulation and verification of time constraints, and which also may be used to generate source code skeletons for an implementation on a MR platform.