[15].Surah Al-Hjir [The Rocky Tract]: Ayat 28-29

Ayat 28. And (remember) when your Lord said to the angels: "I am going to create a man (Adam) from sounding clay of altered black smooth mud.

Ayat 29. "So, when I have fashioned him completely and breathed into him (Adam [PBUH]) the soul which I created for him, then fall (you) down prostrating yourselves unto him." 

Hazrat Abu Hurairah (May Allah be pleased with him) said: The Messenger of Allah [SAWW](PBUH) took hold of my hand and said, "Allah, the Exalted and Glorious, created the earth on Saturday, the mountains on Sunday, the trees on Monday, the things entailing labour on Tuesday, light on Wednesday, He spread out animals of all kinds on Thursday, and created Adam in the afternoon on Friday, and it was the last hour of Friday between the afternoon and the night.'' [Muslim Book 39, Chapter 02, Hadith # 6707]. 

Lesson : as mentioned above in Surah Al-Hjir Ayat 28. "your Lord said to the angels: "I am going to create a man (Adam). What does "Day'' mean, and how long can it be? Its reality only Allah knows. We observe a day of 24 hours. However, the days of the formation of the universe are evidently different from our earthly days. According to the Arabic language, a day may mean just a moment, but also aeons of time. In the Qur'an also, Allah has mentioned that a `day' may be of one thousand or fifty thousand years.