When the mobile phone is set to do not disturb mode, only some contacts can have ringtones after dialing in. The enable sign of "Do Not Disturb" mode is located in the upper right corner of the screen, and there is also a moon sign.
Do not disturb mode has different setting modes. You can set "All Contacts" to allow the following incoming calls, so that contacts in the address book can access even in do not disturb mode, while incoming calls not in the address book will be denied access.
Generally, individuals can freely set the start time of the don't disturb mode when they want to have a rest.
As shown in the figure: