There are two ways.
If you are using sim() to run the simulation, then use [T,X,Y]= sim('model',TIMESPAN,OPTIONS,UT), T(end) will be the stop time that you need.
In the Data Import/Export portion of the Configuration Parameters dialog, check the "Time" option, the time vector will be saved to the variable "tout" in the workspace. When you manually stop the simulation, tout(end) will be the stop time.
Another way is to manually "pause" the simulation, instead of stop the simulation. You'll see the pause time at the status bar (the bar at the bottom of your model window). Then you can stop the simulation.
Or you can put a "Clock" block (in Source library) and a "Display" block (in Sinks library) at the root level of your model. When you stop the simulation, the "Display" block will show the actual stop time.
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