Is it permissible to perform Hajj al-Tamattu‘ on the eighth day of Dhu al-Hijjah, or must it be before that? And what is the evidence for that?

"Tamattu' is performing the two rituals (Umrah and Hajj) in one journey. It requires the pilgrim to exit the state of ihram after Umrah before entering ihram for Hajj. So, if the pilgrim is able to perform Umrah on the eighth day, then exit ihram by shortening the hair, then enter ihram for Hajj from his place, and then go to Mina, there is no harm in that. It is also permissible for him to go directly to Arafat on the ninth day, because going to Mina on the Day of Tarwiyah is only a Sunnah."