I have a field the is a time field. I want to show on a graph the difference between the value of the field at say the beginning of each hour and the end of the hour. Is this possible?

I'm not sure to understand your data model. With Time Series Visual Builder (TSVB) you can produce a chart where you set a interval, take the count of documents for each bucket and then render the difference with the previous bucket.

This example is using the KIbana Flights sample data and rendering both the regular count and the derivative:

Does this help?

No this will not work. What I am trying to calculate is not consistent. Say I have something I can group by and in each of these groups, I there are multiple package delivery times. These do not have a rate of change or anything like that. I just need to be able to find the difference between the first and last of these delivery times for each group and plot that .