A query on permesso di soggiorno

I am an Indian working at the University of Genoa, Italy for last 1.5 years.  My permesso di soggiorno will expire on 30th September, 2018.  I do not wish to renew my Permesso di Soggiorno further and want to return to India permanently.
   I wish to leave Italy on 1st October, 2018. I am planning to board on Air India from Milan to Delhi at 21:00 on 1st October, 2018. Can I do it?  Will there be any problem for overstay by 21 hours?

Sono un indiano che lavora presso l'Università di Genova, in Italia da 1,5 anni. Il mio permesso di soggiorno scadrà il 30 settembre 2018. Non desidero rinnovare ulteriormente il permesso di soggiorno e voglio tornare in India in modo permanente.
Desidero lasciare l'Italia il 1 ° ottobre 2018. Ho in programma di imbarcarmi su Air India da Milano a Delhi alle 21:00 del 1 ° ottobre 2018. Posso farlo? Ci saranno problemi per il soggiorno oltre le 21 ore?

Potential problem as you will, technically, be an over stayer. You should either change your flight to an earlier one or go to the relevant authorities to see if it is a problem.
Perhaps go to the airport and ask there.

I am Italian and this is Italy, hence let me say that you have 99.9999% chance that nobody will care at all. Italian law requires that a permesso di soggiorno be requested by anyone who wishes to stay more than 8 working days (i.e. at the most 12) and is not a EU citizen. This includes all the tourists who have no idea this law exists. Since this law is never enforced it makes no difference. Nobody really cares if an individual is here for a short period more.