I understand you had some issue when you tried to set the simulation time for the Simulink model. You are in the right direction:
1. Configuration Parameters->Solver->Simulation time
2. Set start time=x, Stop Time=y;
3. Click Apply, then click OK.
4. Simulate the model, it should start with x and stop at y.
To see the start time, you can click on Step Forward instead of run, then you will see T=x at bottom right.