This document illustrates how to help Tableau customers publish a view, workbook or Dashboard with data with last refresh time. Customers who need time and date for the data update will benefit.
If you want to add last data refresh (a time stamp) to a view in a dashboard or workbook, please follow the steps listed below:
Open the workbook that contains the dashboard in Tableau Desktop, then navigate to the sheet for which you want to display the time of the last data refresh.
The Data Update Time value depends on the type of connection:
This is from the Tableau community page. Please see https://community.tableau.com/thread/212116 for additional information.