All Dahua manufactured devices have an auto maintenance feature that can cause a device to restart at a set time. The default auto maintain day and time is Tuesday at 2am. Check the auto maintain setting to make sure that the time is satisfactory. Check to make sure the device date/time settings are set correctly. If the unit is restarting at times other than what auto maintenance is set to, try disabling auto maintenance and see if the unit still reboots. Also updating the device firmware to the newest build version can correct a bug with devices restarting.
If the device restarts frequently, refer to the Video recorder is restarting, freezing or locking up (randomly and/or frequently) article for additional troubleshooting steps that may help resolve this issue.