Given log data, calculate the delta between two lines

One of the added values for log parsing is to calculate duration.

Given two log data entries

Start time | Action
---------- | -------
11:59 | start
12:00 | finish

I would like to add a calculated delta field, that given a specific order, calculates the delta (of any given calculation) In the case above we will get

Start time | Action | delta
---------- | ------- | -----
11:59 | start | 00:01
12:00 | finish | 0

Open question:
* Maybe an enrich method that adds information.

No files, tests, or entry points are named. Start by locating the log data model and parsing flow, then clarify ordering, supported calculations, and whether enrichment is the intended API; done means a defined delta field with tests covering the example and edge cases.

Written by the indexing model from the issue text.