Display the Date/Time a worksheet was last updated (tied to external data)

I have some reports that pull data from Oracle into Pivot Tables. Refreshing the data takes about 15 minutes because the queries are complex.

Anyway these are shared reports and typically you only need to refresh them every few hours. Therefore if someone refreshes and saves it I wouldn't need to refresh if I opened it an hour or two later.

Problem is, people don't know when the data was last refreshed so wind up doing it everytime they open the book.

I was looking for an idea to eliminate this problem. What I thought was having the date/time displayed in a cell near the top showing the last time the data was refreshed. Is there a way to do this without using a Macro or perhaps another solution?

Thanks

Seems like a good solution but I am not clear on what I do with that piece of code. My VBA is very limited, best I can do is slightly modify macros that I bulit using the record feature... so what would I do with this code specifically?

Also, seems like this will tell me the last time the workbook was saved which I could work into a solution, but would force me to create separate Excel file for each report. Right now I have 5 reports on one worksheet each, ideally prefer to keep as a single workbook and someone might open the file and update one report, but not all.