Hi Rick,
Your scenario would better be described as an over-allocation of resources. However, assuming activities were not previously planned during the weekends, then it really isn't fast tracking. Fast tracking involves taking activities that were originally scheduled to be completed sequentially and running them in parallel. Crashing is a schedule compression technique where resources are added for the least incremental cost. Even though payroll is not affected in your scenario, there will still likely be some cost involved like office supplies, electricity, etc. In any case, I would say your scenario would be better categorized as crashing rather than fast tracking.