Go into the settings and then the Date and Time settings.
If the box to set the time automatically is checked, the problem is with the network you are connected to. If you're on Wifi, shut off Wifi and reboot again. If you're not on Wifi, call your cell phone company and let them know.
In the meantime, uncheck the box that says to automatically adjust date and time, and set it to the right time. If you travel across a time zone, you'll have to set it by hand.