DND TRacking

Yes, you can implement a simple app to subscribe for user presence notifications. Every time you get a presence event notification, parse the payload and detect if a user DnD presence is "DoNotAcceptAnyCalls" , mark the time and wait until you get an event when the user presence changed to "TakeAllCalls", then calculate the time difference.

Let me know what programming language you are using so I can give you better guidance.