I cannot find a metric that will tell me the max call duration which would include IVR, Agent Talk, Hold, Queue and anything else in between when the call enters and exits.
As far as historical reporting is concerned, you can use the duration value. If the call is being transferred off platform, you may need to build a custom report to combine the duration times into a single value.
Duration
For calls and chats, the total duration of the interaction from the moment it entered the system or was initiated and until it was released.
Note that transferred interactions produce a separate record for each transfer segment, where each record shows duration of the corresponding segment.
As far as real-time metrics are concerned, I don’t see that one exists. This sounds like something you can suggest to Bright Pattern as a Platform Enhancement Request (PER).