This information is available in the default admin reports on the Tableau server: Background Tasks for Extracts
You could also build your extracts with a timestamp field so you have a field in the data identifying the date/time of last update. Note this information is also built into Tableau and should arguably be included on all dashboards, however it may not match your data exactly - i.e. your Tableau extract could refresh but the underlying data hasn't so Tableau is updating against out of date data.
I just had a thought...
If I scheduled another refresh of something that was very, very small (ie a single table with just a few rows), would the start time of this refresh indicate the end time of the bigger refresh that I really care about?
Not necessarily - you could be refreshing both at the same time, you can update in parallel on the Tableau server
Thank you, Andrew, for your creative answers.
However, I don't want to look inside of the extract to see when the extract was done because that presumes that the extract is already done.
I just want to look on the Tableau Server Data Sources Screen (or some other screen, if necessary) and see the start and end time of the extract...or even text that says "Complete".
It seems like something every Tableau Server admin would want to know, especially if they have large extracts.
There's gotta be a way.
There are a few ways, if you're an admin it's very simple and you don't need to look at the data. Check the link I provided earlier to the built in server admin reports, there's one report 'out of the box' that looks at the background tasks, with extracts being one of these.
You can also look at the data sources screen and see the date/time last updated.
The data sources "last updated" time is, I think, when the update started, not when it ends.
But the server admin reports (Status | Background tasks for extracts) shows me what I needed to know.
Wow, some of those extracts refresh quickly. I thought they were taking 15 minutes or longer, but they take under 2 min.