Praise be to Allah.
If a person does not complete the stoning before sunset on the last of the days of at-tashreeq, then he has missed out on the stoning of that day, and he has to offer a sacrifice in Makkah for omitting this obligatory act.
I put this question to our Shaykh, ‘Abd ar-Rahmaan al-Barraak (may Allah preserve him, and he said:
When the sun sets on the thirteenth day (of Dhu’l-Hijjah), the time for stoning has come to an end, and whoever did not stone all the jamaraat before sunset has missed out on stoning. No analogy can be made between this and the prayer.