The Time-Machine is a device which allows any Superstar to travel to any point in time on their Road to WrestleMania (as well allowing an easier way to change in-game decisions).
To get the Time-Machine, play Road To WrestleMania with Christian. Talk to Edge in the south locker room at the Elimination Chamber PPV about the Time Machine. Then, go to the GM Office, and talk to Vince McMahon. You will find out the Time Machine is broken into three pieces.
Look for the Edge and Christian action figures. They are between the bookshelf and the TV. Once you leave, you will get a phone call from Edge. The "Flux Capacitor" (Back To The Future reference) is in the Green Room. The "Phone Booth" (Bill & Ted's Excellent Adventure reference) is in the parking lot. Go to Edge with all three parts to get the Time Machine.