If you are having the audits activated for Project object on that "Active" field then you can query the database to get the dates for all the projects.
select * from CMN_AUDITS
where OBJECT_CODE = 'project'
and attribute_code = 'is_active';
and you can add the following condition for a specific project:
--and OBJECT_ID = <<internal 5 million id of the project>>
But if the audit of the Active attribute is not enabled, then there is no other way.
Hope that helps.