Date Histogram when only have start and end dates (or duration)?

[colings86 (Colin Goodheart-Smithe)]

You might find the following link helpful for this. It is a very similar use-case:

Display concurrency in data on Kibana

I have fields with start date and duration (seconds) representing start and duration of a phone call. I would like to define concurrency (a number) when the same destination (also a field) is active within the same duration. That is if a ncall starts now for 30 seconds and another call to the same destination starts 15 seconds into the first call, concurrency should be 2 for the remaining 15 seconds. How do I define this in Kibana visualization as a line graph over time?

Specifically this post in the topic, but I recommend reading the whole topic to get context: Display concurrency in data on Kibana - #3 by colings86