An alien race appears in front of you

When you are walking along a path by yourself, there is a flash of light and then an alien is suddently standing in front of you. Before you can even say hello it hands you a device with a series of buttons on top (+, -, GO, and a digital display showing today's date and time) and then steps back, smiles, and says "for time travel". Then it vanishes.
What do you do with it?