If you are simulating the model before deploying it to the RT Box, setting that parameter equal to the discretization step size emulates the behavior of the RT Box hardware's PWM Capture behavior.
You can run the model with other values, but they aren't particularly meaningful and won't represent the hardware behavior. The vast majority of the time it is best to create a variable in your initialization scripts and assign it to both settings.
Glad to hear the previous answer was helpful!