D-Link DNS-320L User Manual page 303

Section 4 - Configuration
Click or click and drag your mouse over the time frame(s) you want to set for
constant recording. The selected frames turn to blue to indicate the recording
duration.
Click Save Settings to finish.
Motion Detection Record
Click the Motion Detection Record (red) box to set recording only when motion
is detected by the camera.
D-Link ShareCenter DNS-320L User Manual 297