@Michael Schnider Thank you for reaching out to us, reviewed your query and researched on it, yes you are right we dont have an API to get Scan report time for container registry image vulnerability findings, could be because we don't have an API for Container VA at all
Reference: https://learn.microsoft.com/en-us/rest/api/defenderforcloud/sub-assessments/list?tabs=HTTP#securitysubassessment it can provide list of CVEs as mentioned in this article.
But as per my findings, sending an API request and query ARG: https://learn.microsoft.com/en-us/rest/api/azure-resourcegraph/ might help, but it needs to be tested though if it can provide scan report time information.
Let me if you have any further questions, feel free to post back.