Hi Aaron,
I understand from your query that you're looking to set the stop time for a Step Response plot within the "Model Linearizer" app in Simulink.
To do this, simply right-click on the plot in the “Model Linearizer” window and select the "Specify time …" option. This action is illustrated in the figure below:
Figure 1 Right clicking on the plot to "Specify time”.
You will then be able to define the simulation time. You can specify it either as a time vector or by setting a stop time, as depicted in the subsequent figure:
Figure 2 Setting time as vector or by defining stop time.
Hope this helps,
Regards,
Neelanshu