Any Audit will track its own starts and stops under the Audit Session Changed (AUSC) event. I created an Audit on my local instance and merely enabled/disabled it and then ran the following query:
select actions.name, event_time, additional_information
from sys.fn_get_audit_file('c:\temp\TestAudit*', DEFAULT, DEFAULT) as events
join sys.dm_audit_actions as actions
on actions.action_id = events.action_id;
Here's what I see:
name event_time additional_information
AUDIT SESSION CHANGED 2022-04-10 16:41:58.7244182 <action_info xmlns="http://schemas.microsoft.com/sqlserver/2008/sqlaudit_data"><session><![CDATA[TestAudit$A]]></session><action>event enabled</action><startup_type>manual</startup_type><object><![CDATA[audit_event]]></object></action_info>
AUDIT SESSION CHANGED 2022-04-10 16:42:09.2291167 <action_info xmlns="http://schemas.microsoft.com/sqlserver/2008/sqlaudit_data"><session><![CDATA[TestAudit$A]]></session><action>destroyed</action></action_info>
AUDIT SESSION CHANGED 2022-04-10 16:42:09.2291167 <action_info xmlns="http://schemas.microsoft.com/sqlserver/2008/sqlaudit_data"><session><![CDATA[TestAudit$A]]></session><action>event disabled</action><object><![CDATA[audit_event]]></object></action_info>