The ruling for stoning before midday
Is it permissible to stone after midnight and what is the manner of determining the time of midnight?
Several scholars such as Shafi'i and Hanbali scholars and others have permitted stoning Jamarat al-'Aqaba al-Kubra after midnight of 9th Dhul-Hijjah for the able and unable alike. They based their opinion on the hadith narrated by 'A`isha (may God be pleased with her) who said, "The Prophet sent Um Salama to throw the pebbles before dawn of 10th Dhul-Hijjah and she afterwards performed tawaf al-ifada [Recorded by Abu Dawud. The hadith meets the criteria laid down by Muslim].
Stoning on the days of tashriq
The established opinion for fatwa is that it is permissible for a pilgrim to stone before midday on all the days of tashriq. This is the opinion of groups of scholars from among the Successors and later scholars. Those who have maintained this opinion, substantiated their opinion on text-proofs which include the report of Ibn 'Abbas (may God be pleased with them both) who said, "On yawm an-nahr at Mina, the Prophet was asked about several things to which he replied, 'There is no harm.' A man said, 'I shaved my head before slaughtering.' The Prophet replied, 'Slaughter and there is no harm.' Another man said, 'I stoned after sunset.' The Prophet replied, 'There is no harm.' He was not asked about anything on that day that has either been done before or after its time to which he did not reply, 'Do so and there is no harm' " [Recorded in the Sahih of Bukhari and the Sahih of Muslim. The phrasing of the hadith is Bukhari's]. The evidence from the hadith points to the necessity of lifting harm at the time of stoning.
Based on this, it is permissible to stone on the days of tashriq beginning from midnight. Those who wish to leave on the second and third nights of the days of tashriq may do so.
Since night starts at sunset and ends at true dawn, midnight is calculated by dividing this period by two and adding the result to the beginning of the time of maghrib.