Simulink does not run in real-time. The Simulink model will execute one step of your model, and then immediately move on to the next time step (including plotting scopes if appropriate). Depending on the complexity of your model, this may be slower or faster than wall-clock time.
You could get something approximating wall clock time by using something like this: http://www.mathworks.com/matlabcentral/fileexchange/29107-real-time-pacer-for-simulink.
