mperrotta,
I apologize, the /tm:xxx command line option is only available with the Factory version of our product. Service center was released with the factory command line reference.
What I would suggest is using the /pc:xxxx option instead, which is included in the Service Center product. /pc:xxxx is for pass count, the xxxx value can be from 1-9999. It won't run for a set amount of time but will test the dickens out of components.
Sorry about the confusion, documentation is always a challenge, especially with something as complex as PC-Doctor.
-Fred