The context diagram is also related to a Simulation Parameters definition in the diagram properties. In order for the simulation to begin you need to set these parameters.
Setting simulation parameters
1 Right-click the diagram whitespace, and then click Diagram Properties.
2 Click the Sim Diagram tab.
3 In the Simulation Parameters field, type a name and click the Define button or select the Choices button to reveal existing Simulation Parameters.
Warm Up & Warm Up Units
This allows you to set a warm up period in which there is no data collected during the simulation, set in Week, Day, Minute and Seconds.
Run Length & Run Length Units
This allows you to specify when the simulation will end, set in Week, Day, Hour, Minute and Seconds.
Default Time Units
This applies to the time that appears in the simulation clock.