You can control the execution of test instances in a test set. Using the Execution Flow tab of the Test Lab module, you can specify a date and time, and set conditions for executing a test instance. A condition is based on the results of another specified test instance in the Execution Flow. By setting conditions, you can instruct the Test Lab module to postpone execution of the current test instance until the other specified test instance has either finished running or passed. You can also set the sequence in which to execute the test instances.
For task details, see How to Schedule Test Runs.