Model interchange approaches support the analysis of software architecture and design by enabling a variety of tools to automatically exchange performance models using a common schema. This paper builds on one of those interchange formats, the Software Performance Model Interchange Format (S-PMIF), and extends it to support the performance analysis of real-time systems. Specifically, it addresses real-time system designs expressed in the Construction and Composition Language (CCL) and their transformation into the S-PMIF for additional performance analyses. This paper defines extensions and changes to the S-PMIF meta-model and schema required for real-time systems. It describes transformations for both simple, best-case models and more detailed models of concurrency and synchronization. A case study demonstrates the techniques and compares performance results from several analyses.