There are two possible reasons for the time drift: one is the RTC battery (the CR1220 battery). If you have a multimeter, check if the battery voltage is at least 2.7V. Otherwise you should replace the battery. Second, the DS1307 RTC chip might be defective. If so you can easily replace it. In either case, if the controller is set to perform NTP sync, it should obtain network time every 24 hours to stay in sync with the current time.