Assalamu 'alaykum warahmatullahi wabarakatuh, and thank you for your question. Know, my dear brother, that the 'aqiqah (animal to be sacrificed) is recommended practice slaughtered on behalf of a new born baby during the daytime of his/her seventh day of birth. Al-Bukhari narrates in his Sahih Collection of Hadiths on the authority of Salman ibn 'Ammar al-Dabbi who said that the Messenger of Allah (peace and blessings be upon him) said: ['Aqiqah is to be offered for a (newly born) boy, so slaughter (an animal) for him, and remove harm from him.]. The Sunan Collectors of Hadith narrate on the authority of Samurah who he said that the Messenger of Allah (peace and blessings be upon him) said: [Every boy is pawned against his 'aqiqah, to be slaughtered on his behalf on the seventh day of his birth, he is to be given a name and his head is to be shaved.]. For the the boy two sheep are slaughtered and for the girl one sheep according to the majority of scholars. Al-Imam Malik says: 'One sheep is slaughtered for the boy just like for the girl.'
The slaughtering is on the seventh day of the child's birth according to unanimous agreement among the scholars, and during the daytime according to the Maliki School of Fiqh. If the seventh has passed, the the time for performing the 'aqiqah has passed according to the Maliki scholars. Some scholars regard it as fine to slaughter the 'aqiqah on the second seventh day, that is, the fourteenth day, and if it is not slaughtered on the fourteenth day, then on the third seventh day, that is, the twenty-first day, and if it is not slaughtered on the twenty-first day, then it can be slaughtered any day thereafter. The learned scholar, Ibn Abi Zayd al-Qayrawani, may Allah have mercy on him, says in his famous al-Risalah: [The 'aqiqah is a recommended sunnah. For the newly born child an 'aqiqah is performed on the day of the seventh by sacrificing a sheep similar in age and characteristics to what has been previously mentioned concerning sacrifices for the 'Id.], that is, the 'aqiqah must be free from defects and going into its second year, if it is a sheep, or into its fourth year if it is a cow or into its sixth year if it is a camel.
Moreover, it is not valid to join 'aqiqah and udhiyah (qurbani) for slaughtering one sheep, or one cow, or one camel (for the Shafi'i School of Fiqh it is permissible to do so in the case of a cow and camel). This is because the 'aqiqah is a recommended sunnah practice slaughtered on behalf the new born on the seventh day from the day of its birth and the udhiyah is a Sunnah practice for the one who is able and can afford it slaughtered on the Day of 'Id. Shaykh Ibn 'Arabi says in the al-Qabas fi Sharh Muwatta' Malik ibn Anas: [When a man slaughters his udhiyah on the Day of Sacrifice, and then performs 'aqiqah with it on behalf of his child, it is not valid and does not count), and Allah knows best.