By default, simulations start at 0 s and end at 10 s in Simulink. You can specify other start and stop times in the Solver configuration pane. Please refer to the following documentation for more information:
If you specify the start time to be 20 s and stop time to be 30 s, the signals in the Scope will still be plotted between 0 s and 10 s, but the lower right corner of the Scope window will say "T=30" and "Offset=20".
Thus, if you have set the model to run from 0 s to 100 s, then the whole time range should be plotted on the Scope. Another possibility is that after the 100 s simulation, your Scope is probably not automatically scaled to show the full time range (i.e. it has 100 s of simulation data but is only showing those from 0 s to 10 s). Please use the proper icon in the Scope menu to "Scale X & Y Axes Limits".
