Active Directory group membership timestamp

I am trying to find a timestamp for when a Machine Object was added to an active directory group.

I know the object doesn't change it's "last modified" date when added to a group because it is the group that is being modified. I have a query in SCCM that checks the group every 24 hours. My helpdesk is saying it is not working, and I want to ensure the additions are happening when they say they are.