Temporal correctness is crucial to the dependability of real-time systems. Few methods exist to test for temporal correctness and most existing methods are ad-hoc. A problem with testing real-time applications is the dependency on the execution time and execution order of individual tasks. Thus, the response times for the tasks may be non-deterministic with respect to inputs. Conventional test coverage criteria ignore task interleaving and timing and, thus do not help determine which execution orders need to be exercised to test for temporal correctness. This paper presents test criteria based on mutation to test timeliness. We also show how previously proposed methods in specification based testing can be applied to testing real-time systems.