Time Needed for Creation

There are frum people who find it necessary to distort Torah to fit with scientific theories such as Age of the Universe.  The fact that for thousands of years the Jewish people understood the Six Days of Creation to be six 24 hour periods doesn't stop them from quoting verses, Medrashim and other sources to further their apologetics.  Of course they are aware that the Torah greats of previous generations were well aware of those sources they are quoting.

They wonder:  How could Hashem have created this complex world in only six days?   Even those (not necessarily Jewish) who believe in Intelligent Design maintain that eons were necessary to produce our universe.

The real question is the other way round: Why did Hashem need six days to create the world when He could have done so in an instant?