The eminent Muslim scholar Sheikh Yusuf Al-Qaradawi, states the following:” We are to notify in the very beginning that the six days in which the earth was created are totally different from our normal days. The simple evidence for this is that our normal days have been created after creating the heavens and earth.
Allah says in the Qur’an: “Say: Is it that ye deny Him Who created the earth in two Days? And do ye join equals with Him? He is the Lord of (all) the Worlds. He set on the (earth), mountains standing firm, high above it, and bestowed blessings on the earth, and measure therein all things to give them nourishment in due proportion, in four Days, in accordance with (the needs of) those who seek (Sustenance).”(Fussilat:9-10)
These six days may be referring to six spans of time that are known to Almighty Allah alone or six periods that has nothing to do with the solar system or to six stages that has elapsed and with whose length we are not acquainted.
As for why Allah has created the heavens and the earth in six days while He was able to create them in one second or even less, we are to know that Almighty Allah is Omnipotent and whenever He wants something He just says to “Be” and it is. Allah says in the Qur’an: “And Our word unto a thing, when We intend it, is only that We say unto it: Be! and it is.”(An-Nahl:40)
Here it may be suitable to say that the Divine Wisdom behind this may be to teach people not to be hasty or in a rush but to be patient and to consider every matter before doing it.”