What are DND mode, Smart DND mode and Timed DND?

DND mode: in this mode, the Call reminder, SMS reminder, app notification reminder and mail reminder will cease to remind the user, but the watch will still generate contents and you can view all the unread notification in the notification list.

Smart DND: The DND mode will be enabled automatically once the watch detects you fall asleep. 

Immediately On: The DND mode is enabled immediately.

Timed DND: The DND mode will be enabled in the set time period.