The app offers two date-time fields:
last comment date
first comment date
The custom fields ending with date are native Jira dates and can be compared with time expressions and are therefor most useful in JQLs.
Example JQL queries
Find top discussed issues of the current week
“Comment Count” > 10 AND “Last Comment Date” > -7d
Find all issues that have not been commented on for the last 3 days and the latest comment is not by the assignee
“Comment Count” > 0 AND “Last Comment Date” < -3d AND “Last Commenter is Assignee”=”false”
Unfortunately Jira is currently not able to compare two custom fields of type date with each other. You can find the corresponding feature request here.