Fiqh-us-Sunnah Volume 5, Hajj and ‘Umrah, Fiqh 5.109A.

The three schools of Islamic law hold that the pilgrims must return from Mina to Makkah before the sunset of the 12th of Zhul-Hijjah after throwing the pebbles.

The Hanafi school, however, is of the opinion that pilgrims may return to Makkah betore the dawn of the 13th of Zhul-Hijjah. Leaving after sunset is, however, disliked for it is against the sunnah. but one who does so incurs no penalty.