The subject explains pretty much what I try to say. I have multiple calendars on my phone, I would like to block incoming calls for certain calendars if the time window is blocked.
Open Cortana and then click on Hamburger menu on the right hand top side. Then select quiet hours from the menu and you should see the screen below with the option "Turn on when I have a calendar event marked Busy".. Tick that option and set your respective calendar events to Busy.