Comparing dates between two columns directly on the Airtable interface can be achieved, but it might not be straightforward with the chart extension if it doesn't support that type of comparison natively.
For comparing dates between two columns, you can create a formula field that explicitly compares these dates and outputs the result you need (e.g., days between, earlier vs. later date). Here’s a simple formula for calculating the difference in days between two date fields:
DATETIME_DIFF({Date 2}, {Date 1}, 'days')
This formula will give you the number of days between Date 2 and Date 1. You can adjust the 'days' part to 'months', 'years', etc., depending on your needs.
As for adding a chart extension to your interface, it depends on whether the extension supports being embedded directly or if it's meant to be used as a part of the Airtable dashboard. If it's not possible to add it directly, you might consider using a screenshot of the chart or linking to the chart view as a workaround.