REVIVE A SUNNAH: Restricted Takbeer ‘Begins, on the Fajr of the Day of ‘Arafah (i.e. 9th of Dhul-Hijjah) till the Asr prayer of the 13th of Dhul-Hijjah (i.e. last day of Tashriq).
It is said after finishing the obligatory prayers. It starts from the Fajr of the day of ‘Arafah (i.e. 9th of Dhul-Hijjah) till the Asr prayer of the 13th of Dhul-Hijjah (i.e. last day of Tashriq). It is also said in addition to the unrestricted Takbeer, that is when one finished the obligatory prayer and says “Astaghfirullaah” three times and says “Allahumma anta as Salaam wa minkas-salaam, Tabaarakta yaa dhal-Jalaali wal-Ikraam,” he will start saying the Takbeer.
The above explanation is for a non pilgrim. As for a pilgrim:
It is better for him to be occupied with Talbiyah when he is in state of Ihram till he stoned the Jamaratul-Aqabah on the Day of Sacrifice (10th of Dhul-Hijjah) then afterwards, he starts the Takbeer. He starts saying the Takbeer with throwing the first pebble at Jamratul-Aqabah. [Fatawa Shaikh Bin Baaz]
Sheikh Bin Uthaimeen (Rahimahullaah) said: “The pilgrim starts the Takbeer for Dhuhur prayer on the day of sacrifice (10th of Dhul-Hijjah.” [Sharh al-Mumti’e]
Accordingly, the unrestricted Takbeer and the restricted Takbeer join together in five days, which are the days of ‘Arafah, the day of Nahr (10th of Dhul-Hijjah) and the days of Tashriq.
The 8th Day of Dhul-Hijjah and before that, starting from the beginning of the month, the Takbeer is unrestricted.
To learn more about the restricted and unrestricted Takbeer follow the link below