Unfortunately, the Installation Date/Time is not an attribute reported by the Windows Update Agent to the WSUS server as a permanent value.
There are, however, a few ways you can extract this information other than the computer status information.
If the installations were performed via a Patch Manager task, the installation date/time is available from the Task History, and you can use Task History reporting to extract update/computer installation dates and times.
If the installations were performed by the WUAgent, and recently, you can extract the time the installation event was reported to the WSUS Server from the Update Events tab of the WSUS Server node in the Patch Manager console.
For any installation attempts, you can extract the date/time of installation (or failure) from the Windows Update Agent History report (or from the Windows Update History tab of the Computer Explorer); however, this data may require additional filtering as it will also include installation dates/times for any superseded updates which are no longer of relevance.