Time Tool allows you to change the time and date by clicking on the appropriate part of the time and date display and clicking on the arrows to change the value.
The system clock is not changed until you click on the Set System Clock button.
Click on Reset Time to set the time machine time back to that of the system.
Changing the time can seriously confuse programs that depend on the normal progression of time, and could possibly cause problems. Quit as many applications and processes as possible before changing the time or date.