Showing avergae amount of days an incident is open before being resolved

Content

As the title says really - anyway we can show this? So if we group by hour, how can we see at any hour between the very start and now, how long on average an incident was open before being resolved?

So let's say we ran it at 8am today, the average might be 3.45 days. By 9am we resolved a lot more that came in this morning meaning the average dropped to 3.2.

Any idea?