As per Section 139 (1) "....
every company shall, at the first annual
general meeting, appoint an individual or a firm as an auditor who shall
hold office from the conclusion of that meeting till the conclusion of
its sixth annual general meeting
......."
and one of the provisos to the same Section says ".....
also file a notice of such appointment with the Registrar within fifteen days of the meeting in which the auditor is appointed."
Now,
In case of OPC, the date of AGM is considered to be the date on which the resolution is communicated by the shareholder to the Company as per the provisions of Section 122(3).
Accordingly, In my view, you should file ADT-1 within 15 days from the date on which you have received communication from the Shareholder for the matters which were to passed in the AGM.
Feel free for any more discussion on this.
Regards
Pankaj Khandelwal