Exposing the last time an agent ran successfully
The following script generates a single-record table (you can put in WHERE clause whatever agent you are interested in). Add it to your Tableau workbook as a separate data connection and let it JOIN (join condition doesn't matter since it's always going to have only 1 record). Then you should be able to expose this time to your end users.
SELECT max(end_time) extraction_time
FROM etl_runs a
WHERE agent_name= 'analytics.etl.PdoStar5Agent$'
AND return_code=0