How to add Quiet Hours to your Google Calendar

1. On Desktop, copy the Calendar link from this or other pages
2. Open Google Calendar
3. Click + next to Other calendars
4. Click From URL
5. Alternatively, follow this link
6. Paste the link copied to the URL of calendar field
7. Do not make the calendar publicly accessible
8. Click Add calendar

To our knowledge, it is not possible to do this on Mobile/Tablet currently.