Can one begin a Tamattu‘ Hajj on the eighth of Thul-Hijjah or must it begin before the eighth of Thul-Hijjah? What is the proof for this?

All perfect praise be to Allaah, The Lord of the worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu ‘alayhi wa sallam, is His slave and Messenger.

A Tamattu‘ Hajj means to perform both Hajj and ‘Umrah on the same journey provided that the person should end his Ihraam for ‘Umrah before entering the Ihraam for Hajj. If he joins Hajj with ‘Umrah before performing Tawaaf, then his Hajj is considered as Qiraan and not Tamattu‘. This condition is agreed upon by scholars. If the pilgrim could perform ‘Umrah on the eighth day, ends his Ihraam by shortening his hair and then enters Ihraam for Hajj from his place and goes to Mina, this is alright. In such a case, it is permissible for the pilgrim to head directly to ‘Arafah on the ninth day without having gone to Mina on the eighth because doing this is  a recommended deed.

Al-Baaji said in Sharh Al-Muwatta’: "Maalik was reported to have said that a person who performs ‘Umrah on the day of Tarwiyah (i.e. the eighth of Thul-Hijjah) should not shave his head. Rather, he should shorten his hair and then perform Hajj." Shaykh Abu Bakr said: "Maalik believed that it was better to shorten his hair so as to have some hair to be shaved on the day of An-Nahr."