Evaṃ vattasampattiyā garuṃ ārādhayamānena sāyaṃ vanditvā yāhīti vissajjitena gantabbaṃ, yadā so kissāgatosīti pucchati, tadā āgamanakāraṇaṃ kathetabbaṃ.
Ñ(III,72): To please the teacher by perfection in the duties he should pay homage in the evening, and he should leave when dismissed with the words 'You may go'. When the teacher asks him 'Why have you come?', he can explain the reason for his coming.
Sace so neva pucchati, vattaṃ pana sādiyati, dasāhe vā pakkhe vā vītivatte ekadivasaṃ vissajjitenāpi agantvā okāsaṃ kāretvā āgamanakāraṇaṃ ārocetabbaṃ.
Ñ: If he does not ask but agrees to the duties being done, then after ten days or a fortnight have gone by he should make an opportunity by staying back one day at the time of his dismissal, and announcing the reason for his coming;
Sayādaw U Sīlānanda: [
an opportunity=> to ask permission].
Han: Mahāsī Sayādaw, the same as Sayādaw U Sīlānanda.
Han: I think the Sayādaws’ choice of "asking permission" was based on the Pāḷi word okāsaṃ kāretvā, wherein okāsa means permission.
But when the English sentence is reconstructed it should be clear - to ask permission for what?
I would say that it should be like the following:
[If he does not ask but agrees to the duties being done, then after ten days or a fortnight have gone by he should stay back one day at the time of his dismissal, and ask permission to announce the reason for his coming.]
Akāle vā gantvā kimatthamāgatosīti puṭṭhena ārocetabbaṃ.
Ñ: or he should go at an unaccustomed time, and when asked 'What have you come for?', he can announce it.