Thank you for posting your query on Microsoft Q&A, from above description I could understand that you are looking to find custom analytical rule creation date in Sentinel.
Please do correct me if this is not the case by responding in the comments section.
You could use the built in query from the documentation by hitting "Try it" and get the alert ID:
The systemData tablewould return Azure Resource Manager metadata containing createdBy and modifiedBy information. The created by info is stored for templates and not rules, hence it could not be fetched. Would recommend to go by template creation date or by last modified date.
Please do let me know if you have any queries in the comments section. If you don't have any further queries and the suggestion above answers your ask, please "Accept the answer", This will help us and others in the community as well.
Thanks,
Akshay Kaushik