The following SQL script, executed in SQL Management Studio will return the date of the oldest record:
Select MIN(AET.TimeDetected)
FROM dbo.AuditEvent AS AET WITH(NOLOCK) WHERE AET._id IN (
SELECT _id FROM AuditEvent_IX_SeverityID WITH(NOLOCK)
where [_date_hh] = (
SELECT MIN([_date_hh])
FROM AuditEvent_IX_SeverityID WITH (NOLOCK)
)
)