From Dahua Wiki
How to Set Date and Time on an IP Camera
Note: If your camera is connected to the back of an NVR, you do not need to set the date and time on each camera. The NVR will do that automatically. 1. Download and install ConfigTool from DahuaSecurity.com, under Support->Download Center->Software
2. Run the ConfigTool.
4. Login with the default credentials: User Name: admin Passsword: admin
5. After logging in, go to Setup->System->General->Date&Time
6. Set the date, time, DST, and NTP settings.