The answer from ChrisG (who I think accidentally closed the question?) earlier, which was duly accepted, was:
You can use the search job inspector to see the execution costs of dispatched searches and
search commands. Have you looked at that?
I would also call out that if you're looking for general trends in the time to complete searches, you might get value out of my Search Activity app, which is designed to provide visibility into what users are using the most compute time, what they're doing with Splunk adoption, etc.