How to display timestamp difference from elastic datasource

Dear team, I am trying to add a panel in my dashboard which give me back the time duration for my test. i am very new to grafana.

I am trying to plot time duration (difference between start time and end time), this should be a single panel displaying time duration. The data source i have is elastic and my test sends data during the test, i am trying to display the test duration by subtracting final timestamp (from metrics) with the first timestamp. any inputs here would be helpful


Please post obfuscated sample data as csv?
Version of grafana?
Version of elastic?
Which visualization you want to use?