Can I just change Drupal's default timezone to test to see if some scheduled rules will fire? I need to test to see if some scheduled rules will fire as expected. I cannot change the server time, as I do not have access to do this. However, if I change Drupal's default timezone can I expedite the process? If not is there another way to do this.

Note: I cannot just shorten the schedules rules as they are hardcoded in a contrib module.
I am 95% certain that drupal is using the server's system time so changing the timezone will have no effect as far as rules are concerned.  

Alternatively, you could (temporarily) hack the contrib module to test whatever you need to test and when you're sure things are working, restore the original module when done.