The expression functions seconds(), time() and date(), give time references relative to either universal coordinate time or the base time at which the TestStand engine was initialized. See the description for these functions and their parameters to determine how they can meet your needs.
If you are not looking to reference the time the TS engine was intialized, you may need to get the time your testing begins in order to determine you test time. You could do this in your process model, storing the time reference in a local variable. Remember that in general you should disable result collection for steps you add to the process mdoel.