1. try to restore DVR to factory default like the picture below.
2. you can buy another time battery because maybe battery is dead.
You need open DVR to replace the battery. Here is the method to open DVR.
Picture below shows where the battery is located.
Time on monitor keeps showing the wrong time after several hours you correct it.
Go to the Main menu--System--Net server to set up NTP.
Reboot system after you finishes all.