Show Installed Updates for a Certain Time Period

I believe the report you're looking for is the Windows Update Agent History report.  You can find it under Reporting -> WSUS Reports -> Windows Update.

From what I've seen, WSUS itself doesn't keep track of what installed when (versus it does keep track of when it arrived on the server, when it was approved, etc).  However, each machine does keep track of it in the history and Patch Manager can report on that.

From there you should be able to customize a report and filter it for the specific time frames you're looking for.

Yes - basically WSUS doesn't "care" about install date per machine, and so doesn't store that information in the WSUS database.

One very important point:   The Windows Update Agent History report is one that does show the install date/time of each update..  BUT that report is pulling information from the Patch Manager database (not WSUS).  

The thing that gets that data into the Patch Manager database is an Inventory task that is run against the target machines.   That is not the WSUS Inventory that is used to populate the data for some of the other reports.

If you haven't run an Inventory task against your machines recently, the Windows Update Agent History report might be empty or out-of-date.

This is an example screenshot of the results from that report that jrouviere​ mentioned:

Thanks guys, this definitely helps!