When to Enter Ihram for Hajj Tamattu`
Question

I want to go – if Allah, may He be Exalted, wills – on the seventh day of Dhul-Hijjah to perform Hajj tamattu` [i.e., `Umrah followed by Hajj, exiting Ihram in between]. What should I say when I begin the rituals? Which is better, to shave the head or cut the hair after doing the sa`i of `Umrah? From where should I enter Ihram for Hajj? Do I have to shave my head on the Day of Sacrifice, after stoning Jamrat Al-`Aqabah?
Praise be to Allah.What is Hajj Tamattu`?
Hajj Tamattu` means entering Ihram for `Umrah only during the months of Hajj – the months of Hajj are Shawwal, Dhul-Qa`dah and Dhul-Hijjah – so when entering Ihram for it, one should say: “Labbayk `umratan (Here I am in response to your call, I perform `Umrah).” 
Step-by-Step Guide for Hajj Tamattu`
Shaykh Ibn `Uthaymin (may Allah have mercy on him) said, describing `Umrah of Tammatu`: 
“When the pilgrim reaches the Miqat, he should do Ghusl as in the case of major impurity, and apply the best perfume he can find to his head and beard, then put on the Ihram garments, an Izar (lower garment) and Rida’ (upper garment). It is preferable for them to be white and clean.
Then he should say: “Labbayk `umratan (Here I am in response to your call, I perform`Umrah).” There is no need for him to say that he is connecting it to Hajj, exiting Ihram in between, because he has already formed the intention in his heart that he is going to perform Hajj. So he should say: “Labbayk `umratan, Labbayka Allahumma labbayk , labbayka la sharika laka labbayk. Inna Al-hamd wan-ni`mata laka wal Mulk, la sharika lak  (Here I am in response to your call, I perform`Umrah. Here I am, O Allah, here I am. Here I am, You have no partner, here I am. Verily all praise and blessings are Yours, and all sovereignty, You have no partner).” 
Men should raise their voices when saying this, and it should be understood that no tree, rock or brick hears him but it will testify on the Day of Resurrection that he said this Talbiyah. 
What the Talbiyah means is responding to Allah, may He be glorified and exalted, because the word “labbayk” means: I am responding to You. 
He should continue reciting the Talbiyah until he begins the Tawaf of `Umrah. When he reaches Makkah, he should do Tawaf and Sa`i for `Umrah , shave or cut his hair, and exit his Ihram. Then on the day of At-Tarwiyah, which is the eighth day of Dhul-Hijjah, he should enter Ihram for Hajj only and do all the actions of Hajj. So the one who does tamattu` does a complete `Umrah and a complete Hajj.” (Al-Liqa’ Ash-Shahri)
When to Enter Ihram for Hajj Tamattu`
The one who is doing Hajj Tamattu` enters Ihram on the eighth day of Dhul-Hijjah from the place where he is staying. When he enters Ihram for Hajj, he does the same as he did when he entered Ihram for `Umrah, doing Ghusl and putting on perfume. So he should form the intention to enter Ihram for Hajj and say “Labbayka Hajjan (here I am in response to your call, I performHajj)”, then recite the well-known Talbiyah. 
The scholars of the Standing Committee for Issuing Fatwas said: 
“With regard to the one who enters Ihram for `Umrah from the Miqat, intending to follow it with Hajj Tamattu`, when he has done `Umrah he should exit Ihram. There is nothing wrong with him going to Jeddah or elsewhere, then entering Ihram for Hajj from the place where he is staying after doing `Umrah.” (Fatawa Al-Lajnah Ad-Da’imah, vol. 2, 10/76-77) 
Shaykh Ibn Baz (may Allah have mercy on him) said: 
“What is prescribed for the pilgrim who is not in Ihram is to enter Ihram on the day of at-Tarwiyah from the place where he is, whether he is inside Makkah or outside, or in Mina, because the Prophet (blessings and peace of Allah be upon him) instructed those who had exited Ihram after `Umrah to enter Ihram for Hajj on the day of At-Tarwiyah from the places where they were staying.” (Majmu` Fatawa Ibn Baz, 16/140)
Instructions for Hajj Tamattu` Pilgrims
As you are going to do `Umrah on the seventh day (of Dhul-Hijjah), you should cut your hair after finishing `Umrah, and not shave your head, so that some of your hair will remain for you to shave it off during Hajj. The Prophet (blessings and peace of Allah be upon him) instructed his companions, during the Farewell Pilgrimage, to cut their hair following `Umrah, because their arrival was on the morning of the fourth day of Dhul-Hijjah. This indicates that cutting the hair in this situation is preferable to shaving, and it is better so that the head can be shaved during Hajj. 
What pilgrims do on the Day of Sacrifice 
The actions on the Day of Sacrifice, for the pilgrim who is doing Tamattu` are, in order: stoning Jamrat Al-`Aqabah, offering the sacrifice, shaving the head or cutting the hair, Tawaf Al-Ifadah and Sa`i. This is the best way, because this is what the Messenger (blessings and peace of Allah be upon him) did. For more information, please see the answer to question no. 106594  
If the pilgrim does some of them earlier and others later, or he does some of them after the Day of Sacrifice, there is nothing wrong with that. 
The scholars unanimously agree that it is permissible to delay shaving the head until the last of the days of At-Tashriq , but if the pilgrim delays it any longer than that, then he must offer a compensatory sacrifice, according to some scholars. (See Al-Mawsu`ah Al-Fiqhiyyah, 10/12-13) 
Try to do your Hajj with one of the scholars or seekers of knowledge, so that you can ask him whatever you need to know about Hajj and `Umrah. 
And Allah knows best.