The Time Device or Travel Device is your way to travel back and forth to the time. You will need this all along the game.
How to Get the Time Device
Walk back to the door of the Future Machine, which will be pulsing blue, and click on it to enter. The future will be in ruins. You will meet yourself but 50 years older in the future. Talk to future you and you will get a special time travel device that looks like a golden stopwatch.